almost stalls when it's cold revved
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From: Harrisburg, PA 86 Vert w/ 89 wheels
almost stalls when it's cold revved
weather is cold, start the car, waiting for it to warm up, rev the engine a little to alleviate the boredom but instead of revving up it threatens to stall out.
If I put my foot on the gas slow and steady there's NO problem, it's only when I stab it a little bit too fast.
When the engine warms up enough the engine will freely rev no matter how fast I push down on the pedal.
probable cause?
If I put my foot on the gas slow and steady there's NO problem, it's only when I stab it a little bit too fast.
When the engine warms up enough the engine will freely rev no matter how fast I push down on the pedal.
probable cause?
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From: Plano TX
89 doesn't have the CSV if I remember correctly. Could be a lazy IAC or even a vacuum leak. It sounds to me like this is happening for you mainly in open loop... that's what makes me lean more towards the vacuum.
As for the IAC, when is the last time you cleaned your TB and IAC? That's cheap maintenance and worth a shot to see if it resolves your issues.
As for the IAC, when is the last time you cleaned your TB and IAC? That's cheap maintenance and worth a shot to see if it resolves your issues.
Le Mans Master
Joined: Feb 2006
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From: Louisiana
Originally Posted by LarryK 87
possibly cold start injector?
89 doesn't have the CSV if I remember correctly. Could be a lazy IAC or even a vacuum leak. It sounds to me like this is happening for you mainly in open loop... that's what makes me lean more towards the vacuum.
As for the IAC, when is the last time you cleaned your TB and IAC? That's cheap maintenance and worth a shot to see if it resolves your issues.
As for the IAC, when is the last time you cleaned your TB and IAC? That's cheap maintenance and worth a shot to see if it resolves your issues.
Check for codes and see if any are stored. There are several causes (MAF, fuel delivery, spark, ect.) The cold weather might be effecting something.
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From: Port Charlotte Fl
i believe you are correct on the year ranges which is why i suspected the Cold Start he has an 86. at least thats is what i though his profile showed
it was my assumption ( you know what happens when you assume ) that the CSV ran for a period of time after start up to allow for a richer mixture during initial warm up at coolant temps below 35 or so
course he could also be having a voltage drop issue affcting the MAF as well assuming ( that word again) 86's have MAF as opposed to MAP
pulled the FSM for my 87 and you are correct it (CSV) is only used during cranking.
course next issue again revolves around the CSV maybe the Thermal time switch is bad causing the CSV to stay engaged?
it was my assumption ( you know what happens when you assume ) that the CSV ran for a period of time after start up to allow for a richer mixture during initial warm up at coolant temps below 35 or so
course he could also be having a voltage drop issue affcting the MAF as well assuming ( that word again) 86's have MAF as opposed to MAP
pulled the FSM for my 87 and you are correct it (CSV) is only used during cranking.
course next issue again revolves around the CSV maybe the Thermal time switch is bad causing the CSV to stay engaged?
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From: Port Charlotte Fl
I read up a bit more about the CSV:
CSV circuit is activated only during Crank mode it is controlled by a bimetal switch which opens at the specified ( +35 degF ) coolant temp.
It is also heated by the windings of the thermal switch which allows the CSV to stay ON for up to 8 seconds max @ -4Deg.F coolant temp. On time is inversly portionate to coolant temp ie: warmer coolant temp = shorter on time.
CSV circuit is activated only during Crank mode it is controlled by a bimetal switch which opens at the specified ( +35 degF ) coolant temp.
It is also heated by the windings of the thermal switch which allows the CSV to stay ON for up to 8 seconds max @ -4Deg.F coolant temp. On time is inversly portionate to coolant temp ie: warmer coolant temp = shorter on time.
Le Mans Master
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From: Louisiana
There seems to be a problem with sudden drop in manifold pressure when the ECM is in open loop.
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From: Plano TX
i believe you are correct on the year ranges which is why i suspected the Cold Start he has an 86. at least thats is what i though his profile showed
it was my assumption ( you know what happens when you assume ) that the CSV ran for a period of time after start up to allow for a richer mixture during initial warm up at coolant temps below 35 or so
course he could also be having a voltage drop issue affcting the MAF as well assuming ( that word again) 86's have MAF as opposed to MAP
pulled the FSM for my 87 and you are correct it (CSV) is only used during cranking.
course next issue again revolves around the CSV maybe the Thermal time switch is bad causing the CSV to stay engaged?
it was my assumption ( you know what happens when you assume ) that the CSV ran for a period of time after start up to allow for a richer mixture during initial warm up at coolant temps below 35 or so
course he could also be having a voltage drop issue affcting the MAF as well assuming ( that word again) 86's have MAF as opposed to MAP
pulled the FSM for my 87 and you are correct it (CSV) is only used during cranking.
course next issue again revolves around the CSV maybe the Thermal time switch is bad causing the CSV to stay engaged?
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From: Plano TX
The cold start injector system is only active during cranking. As soon as the engine is running the CSI system times out and is no longer used. The cold start injector is only found on the 85-88 C4's.
I don't think the IAC will come into play here either. The IAC is the idle air control. Once the throttle plates are opened the IAC has no affect. I would check for vacuum leaks though. There are many vacuum lines on these cars and a leak is most noticable with engine operation in open loop..from my experience. Check all the vacuum lines, PVC and hoses, check for leaks around the plenum and runner gaskets. Does the intake manifold leak?
Check for codes and see if any are stored. There are several causes (MAF, fuel delivery, spark, ect.) The cold weather might be effecting something.
I don't think the IAC will come into play here either. The IAC is the idle air control. Once the throttle plates are opened the IAC has no affect. I would check for vacuum leaks though. There are many vacuum lines on these cars and a leak is most noticable with engine operation in open loop..from my experience. Check all the vacuum lines, PVC and hoses, check for leaks around the plenum and runner gaskets. Does the intake manifold leak?
Check for codes and see if any are stored. There are several causes (MAF, fuel delivery, spark, ect.) The cold weather might be effecting something.
I think how I read this might be different than how you're reading it... I was thinking he'd blip the throttle and when it would come back down, foot off the gas, it would stall out trying to reset the idle position.
Now re-reading it, I agree, it's not an IAC issue. Sounds almost like during a cold start (Open loop maybe even) that it's running really lean. I had that issue with a bad program on my prom. So that said, I still stick to my thoughts (and yours too) about a vacuum leak. Like you say, they really come out ugly during open loop.
Last edited by evmlarry; Jan 7, 2008 at 06:48 PM.
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From: Port Charlotte Fl
If this was the case, the car would run rich since the CSV is on the O2 sensor bank. It could also be leaking which would cause the same problem. The CSV is only active with engine temps of <95*.
There seems to be a problem with sudden drop in manifold pressure when the ECM is in open loop.
There seems to be a problem with sudden drop in manifold pressure when the ECM is in open loop.
that issue was Eliminated in our cars with the CSV.
So yep just assumed it was running very rich.
Of course going back to what EVMLarry said a lazy IAC especially while cold and not properly running it'self to the home position could yeild this situation as well ie IAC holding open when it should be closed, too much airflow into the engine could do the same thing as well and would also give you the "To Low Manifold Pressure" condition, and since the IAC is not on a closed loop the ECM would have no idea it was in the wrong position.
all conjecture at this point though.
So Illinest, when you start up in the cold does it smell like it is running rich?
IAC can be eliminated as a possiblity by putting it into diag mode while still warm, then disconnect the IAC connector ( prevents the IAC from operating) after the car has gotten cold see if the problem presents it'self the next day.
Last edited by LarryK 87; Jan 7, 2008 at 07:41 PM.
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From: Harrisburg, PA 86 Vert w/ 89 wheels
doesn't smell like anything unusual in the mornings.
the vacuum lead sounds kinda promising to me. Doesn't the cruise control work off of vacuum? I haven't ever had the cruise control working.
the vacuum lead sounds kinda promising to me. Doesn't the cruise control work off of vacuum? I haven't ever had the cruise control working.
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From: Plano TX
I'd go over all the vacuum lines in which ever fashion you so choose and see if you can identify a trouble spot. I've successfully been able to listen for vacuum leaks with a piece of hose and also with starter fluid both.
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From: Port Charlotte Fl
And can we assume your not throwing any codes?
BTW the CSV will be easy to eliminate as well, simply disconnect it, if the car has no issues next morning, csv or thermal switch, or will not start/very hard start CSV is fine, either way you will know which way things are going.
Also let me ask the obvious here as well, have you checked your spark cable leads? ie very high resistance and/or leaking when cold?
Then same check on your TPS ie bad/erratic resistance when cold.
have you put a vacuum gauge on the engine when cold and monitored engine vacuum, and monitored fuel pressure.
I could see an issue with cold and a vacuum leak ( small but there ) due to thermal contracton, but wouldnt think that would be enough to cause your symptoms, course i could be wrong too just ask my wife
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From: Harrisburg, PA 86 Vert w/ 89 wheels
i've replaced the maf relays (both of em) and the maf itself appears to be in good working order. Also replaced all of the spark making stuff pretty recently.
I've always had a code problem. The car will throw a check engine code 99% of the time when I drive anywhere but when I turn the engine off, jump the connector with my paper clip, and turn the key back on to check codes there's never a code to see. I don't get it.
I've got 150,000 on my fuel injectors which I believe to be all original.
I'll need to refer to the FSM in order to figure out how to check vacuum and and IAC and....
TPS? I can't remember what that is right now. Brain fart?
I've always had a code problem. The car will throw a check engine code 99% of the time when I drive anywhere but when I turn the engine off, jump the connector with my paper clip, and turn the key back on to check codes there's never a code to see. I don't get it.
I've got 150,000 on my fuel injectors which I believe to be all original.
I'll need to refer to the FSM in order to figure out how to check vacuum and and IAC and....
TPS? I can't remember what that is right now. Brain fart?
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From: Plano TX
I just thought of something else also. An intermittent code can also be because a "hard" code isn't being set. That said, you might want to double check all of your connections especially on the MAF stuff you just replaced. Ensure everything is connected tightly. You could simply just have a poor connection in there some where.
Last edited by evmlarry; Jan 8, 2008 at 08:38 AM.
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From: Plano TX
IAC, probably wouldn't worry too much about him.
TPS, you can back probe the connector, or stick a fine needle through the wires, for both the A and B connection (ref FSM cause I can't remember if it's A&B or B&C off the top of my head) and hook up your multimeter and see that you're getting .54v at closed, slowly open the blades to ensure no sticking voltage all the way to WOT where it should be ~ 4 volts if I remember correctly.
