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1991 Chevy K1500 low idle when engine warm


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mhel
New User

Jan 18, 2014, 10:02 PM

Post #1 of 5 (2257 views)
1991 Chevy K1500 low idle when engine warm Sign In

I have a 1991 Chevy Silverado K1500 5.7l TBI actual millage unknown. The truck starts and runs fine when cold, but the warmer the engine gets the more power I lose. It never dies but will only idle around 500 RPM's. Where should I start the troubleshooting process? Thanks for any help you all can give me. I have already replaced the MAF sensor, engine temp switch, new TBI with good flow on injectors, in tank fuel pump.


Tom Greenleaf
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Jan 19, 2014, 3:20 AM

Post #2 of 5 (2234 views)
Re: 1991 Chevy K1500 low idle when engine warm Sign In

? Not sure getting codes if CEL light is on will help much. At least make sure the bulb lights as a bulb check with key jus to "run" position I think it will light.

There's and idle air control (IAC valve) at throttle body that should maintain a proper idle but relies on input signals and connections as well that could confuse the thing.

Should look like this.........


Unknown miles on this? Do you know why it's unknown? It's old enough for plain wiring plug connectors to be weak to make it harder to pin down. I would think a vacuum leak would raise idle.

If no good info or testing can peg it, it can become a parts tossing game that get's expensive. Perhaps clean out EGR and throttle body as well as you can if not codes can help. If pintle in EGR can't seal tight idle would be effected and being cold the enriched fuel delivery could just be covering it.

500 RPM is too low. Alternator, PS, and oil pump would like more if nothing else,

T



Hammer Time
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Jan 19, 2014, 7:47 AM

Post #3 of 5 (2216 views)
Re: 1991 Chevy K1500 low idle when engine warm Sign In


Quote
The truck starts and runs fine when cold, but the warmer the engine gets the more power I lose



It doesn't sound like we are looking for ann idle problem. You might want to measure the backpressure in the exhaust system after it has been running a while.



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Discretesignals
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Jan 19, 2014, 8:34 AM

Post #4 of 5 (2214 views)
Re: 1991 Chevy K1500 low idle when engine warm Sign In

Did you even test anything before replacing parts? This vehicle doesn't use a MAF sensor. What was the fuel pressure, ECT voltage, MAP voltage, 02 sensor voltage, battery voltage, ECM ground voltage drop, and ignition coil KV at the time of the bogging? Is the check engine light on? Any codes? If people would spend time testing, they wouldn't be wasting money swapping good parts.





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kev2
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Jan 19, 2014, 10:35 AM

Post #5 of 5 (2205 views)
Re: 1991 Chevy K1500 low idle when engine warm Sign In

put a vacuum gauge on it - look for vac leaks, watch the reading at idle -

COnfirm - you changed MAF? ECT sensor tell location as there are 2 ? plugs are BLACK WET...dry tan?

Get codes - jump A-B terminals of ALDL tell us what happens...

really easy systwm to work on






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