91 Chevy K 1500 350 idle problem

This is a great informational site. Here is what I have 91 Chevy K 1500 Silverado 350 Automatic 88,000. I have replaced plugs, fuel filter, distributor cap, plug wires, Mapp sensor and EGR valve. It is a great truck but sporatically while sitting at a stop light getting ready to take off I let my foot off the break and it hesitates and almost dies then I give it gas and it runs fine. It only does this a low RPM's and speed. Today I was backing my boat up a ramp; I put my foot on the brake and then let off the brake the Tach went down and it died. IT also did it when I drove up some car ramps to work on the muffler.

Any ideas would be greatly appreciated. The check engine light is not on. If more info would help just let me know.

Thanks in advance.

Could possibly be the O2 sensor, but since the problem seems to occur while on an incline, sounds like its running out of gas maybe??

Could possibly be the O2 sensor, but since the problem seems to occur while on an incline, sounds like its running out of gas maybe??


Thanks CT92. It does it also on level ground. I just recently purchased it and the previous owner said that he took it to a shop and the mechanic changed the EGR valve. It was still having the same problem so 6 months later he took it back to them and they said that it was was his EGR valve again. He explained to them that they had just replaced it so frustrated he took it to another mechanic and they changed the MAP Sensor.

Where is the O2 Sensor located and are there any tests to verify if it is faulty or not?

Thanks again for youe help

DD91

idle air control motor - some automotive stores have it listed as an idle air control valve. it's on the passenger side rear of the throttle body, and has a 4 pin electrical plug going into it. it is what controls the idle speed - if your idle is dropping to the point of the engine dying, that is usually the culprit, since it is how the computer regulates the idle speed

I second the IAC valve. Also make sure it has a clean air filter, I've seen people spend a fortune on parts while using the dirty filter, low rpm can't suck enough air through a badly clogged filter and the engine stalls.

I second the IAC valve. Also make sure it has a clean air filter, I've seen people spend a fortune on parts while using the dirty filter, low rpm can't suck enough air through a badly clogged filter and the engine stalls.

I just changed the air filter. I will change the IAC and post back with the results. Thanks for your help.

I went to pick up an IAC valve today holy $209.00 at NAPA. The partsclerk I was talking to told me to run some Cleen Fuel injection cleaner through it first before I purchased the part. I went thirty miles and will drive some more tomorrow. Hopefully that will be the fix. It didn't do it again but it seems to be sporatic. Who know's?

It died today prior to going to NAPA. I stopped at a stop sign and it just idled down and died. It was pretty warm today (65 degrees) and I am wondering if temperature would have anything to do with it? Also, I am getting poor fuel mileage about 10 MPG.

Thanks in advance

Holy Junkyard! Scrapman, NAPA's got your ball bearings in the crusher! What now!

Tune in next week to see if Scrapman can salvage the IAC or if NAPA gets the green! But wait! does Scrapmans old pal, Sprocket have an IAC on his motor? Will he swap it out long enough to check the problem?

Tune in next week to find out....

<> Tempature eh? Yes it can effect it. Does it happen more often as the engine gets warmer?

Have you checked for small vacuum leaks, hoses, TB, around the intake etc? (with the engine warmed up?)

I like that one JWhite, funny and informative. Got'a love this site!

it hits me every once in a while... i dont know why...it just does. :^)

IAC gets blames a lot but it didnt help on mine - and if you paid more than $50 u got raped.

I have an odd idle that shows up in my 88 2500 and it behaves similarly once u start it and first put into gear...near as I can tell it might be the pressure regulator IN the TBI unit that is going - it literally floods the motor

Touché JW8055!! That was a good one also a good idea. I will try it this weekend and post back.

It does seem to occur more often as it heats up outside. I did check for vaccumn leaks but did not find any.

Simple first, did you replace the rotor when you replaced the distributor cap?

MAdcatter I did replace the rotor when replacing the distributor. Also, tried an IAC unit still did not impact what is happening. Thanks everyone for your help. I will try something else tomorrow.

the fuel pump is bad.

check the pressure.

all the idle problems, and lack of speed and 'ump'
start with the fuel pump.

i just took the very long way around trying to solve a
similar problem; and as they say,
when all else it is not, the only thing left must be it.
well, they are right!

when you try to take the tank down, you may have to
take apart the universal joint. look it over, it might pay you
to replace it while your there.

good luck

you might want to get a competent shop to diagnose this. they have equipment to test the iac, might also be the ect(engine coolant temp sensor), tps(throttle position sensor) or the fuel regulator. or an O2 sensor. throwing parts at the problem gets expensive. for about an hour of diagnostic time a good mechanic will be able to check all these with a good scan tool and fuel pressure gage

if occures on first start and runs rough then smoothes out unhook egr valve and see if runs better gm had problems with egr solenoids opening egr on start up also ck fuel pressure need at least 9psi min 13 max also if ck engine lite on ck codes first, on anything non obd2 if a scanner not on hand go to advance or autozone and let them ck codes or in diag conector under dash cross terminals a and b with key on engine off and count ck engine lite flashes 12 is normal lite will flash long pulse first # and faster second #

kind of a long shot... disconect and plug vacuum to brake booster start your truck apply and release the break maby even drive slowley in your driveway. if it runs ok you have a vacuum leak in the booster



ps do you have any way to get service engin codes to us and remember engin codes only point you in the direction of the problem

unlpug your vacuum line to your charcoal cannister and block it off and see if your hesitation goes away. also when it is cold uplug your temp coolant sensor and see if it starts up and idles good. toivo

You also might want to try setting your idle speed. I know, I know the 'puter handles this. But on throttle body engines the TBI has a set screw that sets the BEGINNING idle. Then the IAC takes it from there. If your set screw has worn down too far, then the IAC has to move too far, too fast causing the engine to die.
I know that I am not calling this procedure by it's right name, but here is how you perform it: Let the engine warm up and then pull the vacuum line off the brake booster, causing an air leak. This will make the engine speed up with the added air and the IAC will slam shut. Turn the engine off. Disconnect the lead to the IAC and plug the vacuum hose back in. Restart the engine and adjust the idle screw. Then shut down the engine and plug the IAC back in.
It's worth a try if everything else fails.