1991 K1500 Rough idle

[branhams4]

CAN'T TAKE IT ANYMORE TURNING TO THE FORUM I have a 1991 k1500 It will not idle without warming up unless I keep giving it gas ,when it is warm it sounds like the engine is cycling high rpm's then low rpm's.When I start from a stop it falls on it's nose for a second then takes off always feels like something is holding it back like no power.I have changed plugs,wires,cap,rotor button,map sensor.I recently checked my egr valve and it seem ok so I took a piece of metal and closed off the hole from my manifold no change in the way it run.I disconnected mt IAC sensor no change,disconnected my O2 sensor no change,changed my fuel filter no change,took my tps off cleaned and put back on no change.When I try to unplug my esc to check the timing it will not idle.

[zmowat]

Did you have a check engine light come on when the problem initiated??? I would check the voltage of the ETC (coolant temp sensor) it is possibly out of whack. You need a multimeter and the proper specs. For a quicktest voltage should be higher with a cold engine, as engine warms resistance increases and voltage drops. If the truck runs good after it is warm, it is possible the sensor has a problem only at a specific temp/resistance/voltage level. I have seen it happen before.

[K1500_4x4_Custom]

I have Kinda the same problem, been tring to fiqure it out myself, only in my case it seems to Cycle in the 200-300 RMP range (i.e. 750 to 1000 then back to 750 then up to 1000 ) not correct numbers just est.s even after it is warm, and the "Service Engine Soon" light comes on and off intermitatly. It never Dies or "idles rough" in the sense of it "missing" but acts more like the computer is adjusting for a failing sensor somewhere, any one have a idea where to start looking?

[toivo]

Originally Posted by branhams4

CAN'T TAKE IT ANYMORE TURNING TO THE FORUM I have a 1991 k1500 It will not idle without warming up unless I keep giving it gas ,when it is warm it sounds like the engine is cycling high rpm's then low rpm's.When I start from a stop it falls on it's nose for a second then takes off always feels like something is holding it back like no power.I have changed plugs,wires,cap,rotor button,map sensor.I recently checked my egr valve and it seem ok so I took a piece of metal and closed off the hole from my manifold no change in the way it run.I disconnected mt IAC sensor no change,disconnected my O2 sensor no change,changed my fuel filter no change,took my tps off cleaned and put back on no change.When I try to unplug my esc to check the timing it will not idle.

if your idle does not change when to put a plate over the intake hole you have an intake vacuum leak. since you have a throttle body, chevies are known to suck in the base gaskets on the throttle body. spray carb cleaner at the base of throttle body and the idle speed should change when you find the hole.toivo

[prankstar]

mine did something like that and all i did was replace the TPS, then fine. I think you may want to double check that also. But I also think that you should get a trouble code for whatever problem you are having and that should solve your struggles unless it is the base gasket.

[dirt49er]

i would replace the throttle position sensor, and if theat doesnt work, hook the red brick up to it and check it out. if that doesnt work you can always get an edelbrock or holley throttle body

[branhams4]

Thanks for the advice I checked all sensors with a volt ohm meter they all checked ok.While checking I unplugged the temp. sensor and the truck Idled great then I drove the truck no hesitation ran great but with some pinging not much though.I bought a new sensor and installed it but the truck started running rough again,I advanced the spark and got rid of the falling on it's nose when I give it gas but now it pings very bad.Any thoughts on what else I should try.

[drgnslaayer]

LOW AND BEHOLD... someone with the SAME problem I have...
get this...
NEw Fuel Filter... NEW Exhaust...
rebuilt distributor..
EVERY SENSOR NEW
3 sets of plugs and wires...
new timing chair and gears
2 sets of injectors...

need I go on??? now... I out this afternoon... the guy who owned it 2 ppl ago... had this problem...tightened down the intake and it stopped... AHHA!!!!! sounds to me like a leaky intake gasket between 2 ports ( outter leak checked with ye old starting fluid... nothing changed) BTW... did I mention new computer and PROM chip also?

[drgnslaayer]

I am changing the intake gasket probably this weekend.. ill let you know what happens...