# 85 Suburban engine idle quits



## Dakine

hey guys I have a problem with my latest truck and I'm hoping maybe someone has a suggestion!

its an 85 Chevy Suburban, nothing tricked out, all stock as far as engine and drive train go.

starts fine, run it for a few minutes and then it dies. this is NEW, it used to just idle fine for however long I let it.


I first thought oh, its out of gas and i added fuel, nope. same thing
then I thought maybe vacuum except it starts right back up, so it seems to me whatever vacuum prob may be happening should still be there
then I thought electronics... and same thing as above, it starts right back up and runs a few minutes more and dies. if it was a component warming up or overheating, it already did that, starting again should be in the same condition.
fuel filter seems a no-go because if it was clogged and choking fuel why restart and run another couple minutes before repeating the new behavior?

any ideas?


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## Cotton

Does it die while driving after a few minutes? Or just sitting at idle? What is the actual engine temp, does it get up to normal operating temp? Or is this with a cold engine?

The only time I’ve ever seen something this strange… somewhere in my wiring harness I had a ground and a hot interacting. The whole harness would mimic a capacitor, would build a charge over time and skew fuel mixture and timing, killing the engine. This problem was very intermittent, once every couple of months. I never found where the problem was, just converted the engine to a carb.

How does the engine sound when it dies, normal, like turning off a switch or rough?


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## Dakine

Cotton said:


> Does it die while driving after a few minutes? Or just sitting at idle? What is the actual engine temp, does it get up to normal operating temp? Or is this with a cold engine?
> 
> The only time I've ever seen something this strange&#8230; somewhere in my wiring harness I had a ground and a hot interacting. The whole harness would mimic a capacitor, would build a charge over time and skew fuel mixture and timing, killing the engine. This problem was very intermittent, once every couple of months. I never found where the problem was, just converted the engine to a carb.


it's a driveway queen at the moment, I don't have tags so I've just been doing small time maintenance and upkeep and then this thing started.

it's very reproduceable, like turn it on and wait 2 or 3 minutes and there it is, restart it and there it is, etc. so not quite as random as the problem you had.

Edit to add: there's nothing special when it dies. no harsh idling, no backfires, just dead stop instantly.


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## Balls004

Fuel filter first... Get enough rust, trash etc. in one, and it will start, run, and then die.

I'm assuming that it's a throttle body injection system, next thing I'd check is the Idle Air Control (IAC). They will get a carbon like build up around the pintle and seat, and cannot control the idle correctly. Unscrew the IAC motor, and clean the pintle and the seat in the throttle body with some carb cleaner. You'll probably need a pair of forceps or thin needle nose pliers and a small piece of rag to clean the seat. 

If you have a timing light, you can use it to look at the spray pattern of the injectors if it's throttle body injection. Hook the timing light up like normal, and then point it inside the throttle body on each intake runner. You should see a nice cone shaped spray... Any spotty looking or rough look to the spray cone it means the injector is clogged. Injector cleaner may or may not help. It's usually easier to just replace the injector.

Hope this helped...


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## JustCliff

Check the voltages on your coolant temperature sensor. It should be located near the upper radiator hose outlet on the engine intake manifold. It is a 2 wire connector. 
It's about $16 bucks at Autozone. 
It sounds as though when your engine gets warm, the sensor is telling your computer that the engine its freezing cold. It's dumping fuel to keep it going. 
If that is the problem, you will also now have to change your O2 sensor and your plugs Because you have been dumping unburned fuel down the exhaust.


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## Tirediron

If it is stock, an 85 GM truck has a carb, if changing the fuel filter ( the filter may be plugging enough to drop the fuel level enough to lean out the mixture, but allowing the bowl to fill back up for a restart, change the filter anyway, the new fuel mixes are filter pluggers) doesn't solve the problem, the distributor is the next suspect, the module could be going away or the pickup coil, If the distributor has the early attempt at electronic timing control replace that module with a standard fixed timing model. If you get into the distributor consider adding a remote module harness kit. them a module change is really easy.


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## cowboyhermit

Especially if it has been sitting my first thought is it sounds exactly like a float issue. Try feeding it some gas through the throttle body (carefully) when it begins to die (or potentially starting fluid) to see if it is fuel related.


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## readytogo

Ignition Control Module (ICM),have it tested with meter, they are not that expensive and if you need one please get and acdelco or Delphi brand from http://www.rockauto.com/ or at least check the parts numbers on their site, also check fuel pump pressure at tbi .you probably have an 305 or 350 eng 
http://www.doityourself.com/stry/2-symptoms-of-a-deteriorating-ignition-module


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## jimLE

ok Dakine.it looks like to me.that you dont get it out on the street and drive it any.now im wondering when it last saw any driveing time on the streets.if it's been over 2 or 3 months,or what ever.wait untill you know that you wont get pulled over for no tags.then drive it around for 10 to 20 minutes.on account there could be some build up in the fuel injector.and if you drive through a area where there's no one else around,give it the gas.on account that might blow out some of the build up..someone suggested fuel cleaner.thats a good idea to go with.especilly if you drive it any..


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## Marcus

It could be the float sticking. 
One thing I came across years ago is old rubber vacuum lines can get too flexible so that the vacuum pump causes the vacuum lines to kink.


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## mosquitomountainman

If it has a vacuum advance you might try unplugging it (plug the hose) and see what happens. Sometimes the wire going to the pickup coil breaks internally and when the vacuum advance turns the base plate it loses the connection.

Do not trust the testers part stores use on electrinics. They are horribly ineffective. I had a module that tested good but was defective. I put a new one on and the vehicle worked fine. Similar story with a neighbor's truck. I have lots of other examples as well. If it tests bad it's probably bad. If it tests good it may still be bad.

Good luck and keep us posted.


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## Dakine

cowboyhermit said:


> Especially if it has been sitting my first thought is it sounds exactly like a float issue. Try feeding it some gas through the throttle body (carefully) when it begins to die (or potentially starting fluid) to see if it is fuel related.


that's the problem though... there is no "starts to die" it's instant! like it was never running in the first place. WHACK! done. and then restarts just fine which is why fuel and electronics puzzle me, because 5 seconds ago whatever was killing the engine should still exist.

please dont get me wrong I appreciate the advice and replacing all of that basic spark system is on the menu anyway, I've already started buying all the cap wires, plugs etc.. I need to get the module though, and I need to figure out how to get my rather tall self into that raised engine compartment without having to fold up like a pretzel. that's actually the worst part of this


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## cowboyhermit

Well, if it's that fast to start/stop then others may be right about it being electronic. Modules can fail like that, it can be rather maddening, though I don't recall ever having such a repeatable problem with one, they were always erratic IIRC.


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## Oomingmak

Had something similar happen on our suburban.......... ended up being the fuel pump.


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## Dakine

mosquitomountainman said:


> If it has a vacuum advance you might try unplugging it (plug the hose) and see what happens. Sometimes the wire going to the pickup coil breaks internally and when the vacuum advance turns the base plate it loses the connection.
> 
> Do not trust the testers part stores use on electrinics. They are horribly ineffective. I had a module that tested good but was defective. I put a new one on and the vehicle worked fine. Similar story with a neighbor's truck. I have lots of other examples as well. If it tests bad it's probably bad. If it tests good it may still be bad.
> 
> Good luck and keep us posted.


good advice and my first instinct is to tear out and replace everything replaceable. even if a hose is good I'm at least starting over from a new baseline before it eventually cracks and fails.

tomorrow morning I'm going to the local autozone and getting the last of the spark parts. I'm not sure what to do about the carb, it's been ages since I've messed with one... like high school, and I'm not excited about starting on this one LOL!

i'm tempted to buy a rebuilt carb and just cough up the core charge and have this factory carb rebuilt as a standby. this should be a legit Holley but I need to verify that too.

Also, I need to do all the fluids. ALL of them. and I've got aftermarket bolt on's to... well, bolt on LOL!

I've got my work cut out


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## Tirediron

what fool took the real carburetor off and put a Holley on??? 
Holleys work well when they work, but they are fussy about tiny bits of dirt and especially dryed fuel, 

Rochesters the carb built specifically for the small block chevy are more efficient and way more forgiving not to mention tunable. 
and most of the time you can reuse the gaskets


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## mosquitomountainman

Agree on the Holley carb. switch. I've done hundreds of quadrajets. They have their quirks but overall they're about as good as they get for a small block. The main thing is to be sure the metering wells are sealed. They'll use a lot of gas and have idling problems (rich mixture and rough idle) if the metering wells leak.

The old Ford four barrels and the Chrysler Thermo-quads are junk (IMO) and ripe for replacement with Holley carbs. Both of them caused far more problems than a Holley. Holleys have their own set of peculiarities to deal with.

I did have a 350 Chev. pickup that I had to drill the jets out on but it wasn't doing what yours is. This one had a hesitation on acceleration that nothing would cure. We even pulled in another identical pickup in and I began switching parts. Whatever I took off truck #1 worked fine on truck #2 but nothing cured the problem truck #1 was having. I finally drilled the jets out another size larger and truck #1 began performing like a new one.

Also, I've had a lot of problems with manufacturers rebuilt carbs. If you can rebuild the one you have you might fare better. (As a mechanic I'd only use a parts store carb. if there was something broken or stripped out on the original carb.)

Another hint, do your changes one piece at a time. That way if you create new problems you'll have an easier time correcting them. For example: I once changed the spark plugs on my Ford pickup at the same time I put a new (Holley) carburetor on it and put in an aftermarket electronic ignition conversion. I was sitting at a stop light in downtown Kalispell early one morning when a cop drove up beside me. My truck was idling smoothly then just suddenly let out a very loud backfire. It echoed off the buildings on main street and the cop was still sitting there looking for the source of the "gunshot" while I quietly motored away. It did it several more times and I finally decided to change the plugs again. That fixed the problem. I'd tried out some of the JC Whitney "lifetime" spark plugs and evidentally one of them caused the problem. I threw them away and put stock plugs back in it.


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## Dakine

yeah we do the same thing at work changing one thing at a time if we can, troubleshooting computers and applications can be as bad or worse than cars.

pouring rain today, I guess the parts swaps will have to wait until next weekend.


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## readytogo

Dakine said:


> hey guys I have a problem with my latest truck and I'm hoping maybe someone has a suggestion!
> 
> its an 85 Chevy Suburban, nothing tricked out, all stock as far as engine and drive train go.
> 
> starts fine, run it for a few minutes and then it dies. this is NEW, it used to just idle fine for however long I let it.
> 
> 
> I first thought oh, its out of gas and i added fuel, nope. same thing
> then I thought maybe vacuum except it starts right back up, so it seems to me whatever vacuum prob may be happening should still be there
> then I thought electronics... and same thing as above, it starts right back up and runs a few minutes more and dies. if it was a component warming up or overheating, it already did that, starting again should be in the same condition.
> fuel filter seems a no-go because if it was clogged and choking fuel why restart and run another couple minutes before repeating the new behavior?
> 
> any ideas?


Don`t go crazy trying to replace everything, try testing a few things first fuel pressure at TBI or carburetor, ignition module, dirty fuel filter; vacuum lines will cause a miss but will not stop the eng from running; carburetor issues and ignition are basically the same symptoms, my advice is to get a good repair manual with an ignition / testing section and a good digital meter.
http://www.doityourself.com/stry/2-symptoms-of-a-deteriorating-ignition-module


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## Tirediron

While readytogo's post contains sound advice on most troubleshooting, electronic parts often pass multimeter testing but fail load testing, and unless a person is load testing HEI ignition modules all day, it is not worth the time, a know good replacement is the easiest solution. pick up coils are the hardest to diagnose until they fully fail and a pain to change because the distributor must be removed from the engine. a complete spare known good distributor would be a really handy part to keep on hand.


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## Grimm

This sounds similar to the issues I had when I was trying to get the Ghia running back when I was 19. It had been sitting a while in the garage only to be started once in a blue moon while it sat in the driveway but never driven.

I know a Ghia is nothing like a Chevy but do me a favor and check the bottom of your gas tank. Because the car sat the gas in the tank jellified at the bottom. The car would start up but stop as soon as the gas jelly got in the lines. It would run back in the tank and the process would start again. I had to replace the tank and the fuel lines.


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## Dakine

Grimm said:


> This sounds similar to the issues I had when I was trying to get the Ghia running back when I was 19. It had been sitting a while in the garage only to be started once in a blue moon while it sat in the driveway but never driven.
> 
> I know a Ghia is nothing like a Chevy but do me a favor and check the bottom of your gas tank. Because the car sat the gas in the tank jellified at the bottom. The car would start up but stop as soon as the gas jelly got in the lines. It would run back in the tank and the process would start again. I had to replace the tank and the fuel lines.


absolutely anything is possible. the cirumstances are somewhat different though and the replacement to factory (or better) new parts is already on my to-do list so I'm going to roll with that first but checking the gas tank will surely get moved up the list if the problem persists through all the new spark parts.

I also wouldn't mind doing a skid plate to protect the fuel tank at some point. I guess I really should start a wishlist for the truck.


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## readytogo

Have been using this tool for many years now and has saved me lots of money ,instead of replacing parts ,I check them.
http://bristolautomotiveparts.com/product/sensor-tester-plus-cp9080/
Cheaper on ebay or amazon.
But if you know how to use a digital millimeter and follow service manual specifications you can fix anything.


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## Dakine

Thank you, that looks like a very handy tool!


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## readytogo

Dakine said:


> Thank you, that looks like a very handy tool!


You`re welcome ,hope I could help you some and always remember that is easier to eliminate the cheapest problems first ,for all my vehicles and even lawn machines I always get the service manual ,something to think about.
good luck:beercheer:


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## zombieresponder

Ditch the Holley and put a quadrajet back on it. My '77 had a holley on it when I bought it...probably the most temperamental carb I've ever had to fool with. That said, when it was right, it was *right* and the old truck ran like a cat with turpentine on his tail. The quadrajet is a better carb though.

I didn't catch how long it's been sitting, but the tip regarding the gas tank is a good one. The previously mentioned '77 sat for a few years and the tank rusted up pretty badly, which partially plugged the fuel filter. Also check the ignition module and all the connections.


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## Dakine

I was mistaken before, it is a Quadrajet, it's been a very long time since I did much wrenching around on engines, so I'm kind of figuring out or relearning a lot of this as I go.

speaking of going, off to parts the store to get fuel filter, cap and I guess that's an HEI and a module.


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## Oomingmak

Did you get this problem sorted out?


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## Dakine

No, everything at work went sideways with an acquisition and other than Thanksgiving I've been hard pressed to get a day off and working some late hours into the night too.

I just don't have time to do both, I really wish I had a decent mechanic nearby that wanted to pick up some side work, that would be perfect.


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## Cotton

That era engine is simple... Either it's missing fire or fuel... force feed it one ore the other...  then you'll know what's wrong!


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## Dakine

Cotton said:


> That era engine is simple... Either it's missing fire or fuel... force feed it one ore the other...  then you'll know what's wrong!


LOL! I know it's pretty basic with those years. but like I mentioned in an earlier post there's no hesitation, wheezing, or any indication whatsoever that it's gonna have a problem, it just shuts off instantly.

Which after someone else mentioned the module, that reminded me that an old 75 Chevy stepside I had (man I loved that truck) had a similar issue, $20 module later and boom, problem solved!

I suspect this is going to be the same thing, but I want to replace all of the spark pieces anyway, I've bought all the parts I just don't have the time or the nimble swivel jointed wrists and elbows to crawl around in the engine compartment like I used to, especially on a raised vehicle.


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