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Rough idle when cold

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Sganderson

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Hello all,
My 88 jimmy sounds as if it's missing or studdering whenever it idles cold. Seems to go away when engine is warm. It will also stall if if I don't hold the throttle down until it warms. It's never stalled other than after a cold start . There's also a smell of gasoline in the exhaust. I've adjusted the timing, replaced the O2 sensor, spark plugs and wires, distributor cap and rotor, and ignition coil to no success besides it running better overall. I've checked for vacuum leaks around the throttle body and body spacer with wd40 and found nothing. The only thing I can think of is a vacuum leak somewhere or a failing ignition control module. Anyone ever had this problem before? Thanks
 
Sounds like you covered the basics..I doubt the ignition module would cause that,they usually either work or dont,or crap out completely intermittently..


Only things I could say to look at is maybe the EGR valve is getting vacuum when it shouldn't when cold,or is sticking open slightly..it could be flooding when cold,if it has a fuel pressure regulator I'd pull the vacuum hose off it and see if any fuel comes out of it,if so,the diaphram is ruptured in it,and it'll suck raw fuel into the intake..


I've seen a few engines skip only when cold when a head gasket or cracked head leaks slightly after shut down,and lets coolant build up overnight in the cylinder,just enough to foul the spark plug,then it'll burn off as it warms up and the leak "seals" itself from expansion..if this is the case,you may notice the engine cranks normally one or two revolutions,then "stops" or hesitates,then cranks normal and fires up..and you may see white smoke for a few seconds to a minute,it can cause it to stall too until the coolant burns off..keep an eye on the coolant level..it wont show as a big leak,it'll take a long time for it to drop usually..
 
I have an 88 Suburban that started doing the same I noticed I had some vacuum lines that where rotted so I replaced them I cleaned the throttle body with out and it had been working fine until a couple of days ago it started doing it again taking it to the mechanic to see if he can trouble shot it for me I'll repost to see what he comes up with any luck with yours
 
Thanks for the replies. No luck yet, I replaced a dried up pcv valve and a couple rotted vacuum lines. Still skipping a lot when it's cold and only randomly after its warm. I haven't checked the egr yet and I haven't had to replace any coolant in over a year so I wouldn't think a coolant leak Is the problem. I'm gonna check out the fuel pump, filter, and relay sometime. I'm going to figure it out one way or another.
 
ActuAlly I just thought of this, I noticed I had an exhaust leak where the manifold connects to the exhaust pipe. This is right before the O2 sensor. Now could that leak make it look lean to the O2 sensor and in turn cause the computer to dump extra fuel causing it to misfire? Later on when it warms up the leak seals itself somewhat causing less frequent misses. Random thought, but makes sense to me.
 
Doubt it, I've driven mine half way across the country with the O2 unhooked due to a broken connector clip, pulled it out while trying to figure out a different problem at that time.
 
Unhook your coolant temp sensor and see what it does once. It'll obviously light up the check engine light.

We toyed with that on mine for a bit, I ended up replacing it and ended up not being the problem, but it did make if driveable. I think mine ended up being a vacuum hose was on the wrong port of the egr vacuum solenoid.
 
If anything, bad idle when cold but not warm means your O2 sensor is working, not failed. Hate to see good parts swapped out.
 
Haven't figured it out yet. I want to also check egr, ecm and coolant temp sensor sometime, maybe even my fuel system. My father swears up and down there's gotta be a vacuum leak somewhere. I can't run codes bc my service light only comes on when it wants to. It used to come on when I turned the key now it don't. It randomly comes on while I'm driving sometimes so there's that.
As for the swapping out of good parts, no need to fret. I am keeping and stockpiling everything I change. I bought this truck two years ago and I have no clue what the other guy has done to it beside put a crate motor in it and the body was beat up spray painted flat black. Since then, I've done various minor things to it. I had the body redone and painted. Put steel wheels on it with 35's bfgs at, and a 4" lift. Kind if a mini restoration? Personally I like knowing exactly what I have in it. So I don't really mind buying new parts for it even if not really needed, especially since most of the small parts and sensors are $40 or less. Plus I enjoy learning how to replace and repair. It's all a learning experience for me plus I get to drive an awesome truck.
 
Sganderson said:
I can't run codes bc my service light only comes on when it wants to. It used to come on when I turned the key now it don't. It randomly comes on while I'm driving sometimes so there's that.
Click to expand...

Codes are stored for 50 starts so they you should be able to read them.
 
If the check engine light isn't coming on when the key is turned to run (not start) need to figure out why. That's pretty much the first check of the system.
 
Could be a wiring issue, loose bulb holder, PROM, ECM, you name it. Could very well just be the bulb is dead, but if you can't check codes because the bulb is failed or intermittent, you lose a pretty significant diagnostic tool.
 
Your problem sounds similar to mine, here is what I have tried with results.

When temps reach about 45 degrees or lower mine has issues. So today I replaced one of the vacuum lines with some that was laying around, and replaced Coolant temperature sensor.

This did smooth out my trucks idle, but was burning far more fuel during warm-up, and tripped a code until warm (never did that before).

Once engaged into gear it would stall. Once it was underway it would have a gnarly miss with hesitation till optimal operating temperature.

Hopefully between enough of us having similar issues we can resolve this problem.

Also cleaned the IAC, but going to replace this anyways.
 
Ok well I replaced the coolant temp sensor with no success with the problem I'm facing. I did notice that the misses go away when my truck is in gear. It only happens in park and neutral. I swear I'm eventually going to auto zone and let them try and pull codes so I can narrow this down.


Quick question. Would it be better to go ahead and replace my egr valve or take it out and give it a good cleaning if the diaphragm isn't ruptured?
 
I was having similar issues. Mine ended up being a bad battery. It would start without hesitation, but caused all kinds of weird symptoms. Just something to think about. The battery was fairly new as well. Throw another battery in there just to rule that possibility out. I messed with mine for a week before finally figuring it out.
 
Quick update

Took throttle body off and cleaned it. Went ahead and replaced my egr bc old one had a ruptured diaphragm. Also bought a new iac valve which I haven't installed yet. Overall the engine is running better but still cold start low idle sputtering.

Here's the tricky part. I went around with my multi meter checking for voltage. Fuses look good. Coolant temp reading 5v. Iac terminal reading nothing. I checked all terminal pins with engine running and got nothing. Couple that with no service engine light. Bad ground? Bad ecm? Not sure how to check this with the inability to pull codes. Any ideas?
 
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