1989 c1500 fast idle

[johnnymcbrown]

My 1989 chevy c1500, 5.0l engine has a very high idle speed. I replaced the 6 sensors for the TBI and it is still has a very high idle. I hooked up a digital timing light and the RPM was 2200 and the timing mark was 25 degrees. I don't know the procedure for checking and setting the timing, if someone would tell me I'll try to set that. I did reset the ECM , same fast idle. The EMC flashed 12 when checked ( and I unplugged the temp sensor which resulted in a 15 code so, the EMC seems to be working)

help would be appreciated.

[grimesjm1]

i'm not saure on the timing specs for the 5.0, i have a 5.7, but you need to unplug the electric spark timing advance wire to get an accurate timing reading. on my 94 z-71, it's a tan wire black tracer under the dash on the passenger side. that is why you may have been getting a reading of 25 degrees. if the 5.0 is the same as the 5.7, correct timing with the est wire pulled should be 0.

[homefree]

I have the same kind of truck that had a idle problem and what i did was replace the IAC valve that screws into the side of the throttle body on the passenger side of the truck and it worked great for about 1 hour then after that it wouldn't idle for crap. To make a long story short what happen was the NEW IAC VALVE that i put in came apart inside the throttle body, if you look at it there is a pin at the end of this IAC valve that goes in an out to control the idle and that had came unscrewed from the IAC valve . So what i did was put some LOC TITE on the treads of that pin and srewed it back in to the IAC to keep it from coming back out. Another thing to look for is when you take that IAC out look for carbon build up where that pin would go into the throttle body . There maybe carbon in the way from that pin going in and out all the way. Another thing to look for would be a vaccum leak by the base of the throttle body. Good luck. keep me up dated. Thanks

[johnnymcbrown]

When I observe the 2 injectors, they both are really spraying a lot of fuel. With ignition on, engine off, the 2 injectors are not leaking. How do you determine if the injectors are bad?

[johnnymcbrown]

Originally Posted by grimesjm1

i'm not saure on the timing specs for the 5.0, i have a 5.7, but you need to unplug the electric spark timing advance wire to get an accurate timing reading. on my 94 z-71, it's a tan wire black tracer under the dash on the passenger side. that is why you may have been getting a reading of 25 degrees. if the 5.0 is the same as the 5.7, correct timing with the est wire pulled should be 0.

Thanks for the reply, If I disconnect the ECM wire at the distributer, and with the engine idle at ??RPM then the timing should be 0..right?

[jkinney]

Hey HOMEFREE, I'm not sure if I'm reading your post correctly, but when you replace the IAC, your supposed to measure the distance of the replacement and set to 1.125 inch. If you had it out too far, that would explain why it fell out. And under no circumstances are you to Loc-tite them. After mounting, cycle the ign key on for 10 sec, then off for 10 sec. Start and let idle for 5 min, then turn off for 30 sec. Should be good after that.

[homefree]

Hey jkinney you are right on the loc tite. Let me explain this a little better. I'm not the best at explaining things. On the IAC it self the pital fell out so to keep that from happening again I loc tited the pintal back into the IAC then i screwed it back into the throttle body. I did read on another fourm some were on the net that this is a common thing, But by all means don't loc tite the IAC it's self into the throttle body, but set it the way jkinney has said to that is correct.

When i bought my truck used from a friend he said he had blown it up and it was knocking and it was smoking alot. Well i ripped into it and had the same symptom it was getting a lot of fuel you could see that it was just dumping it into the throttle body and ran like crap so the first thing i changed was the fuel pressure reg and that didn't help I did a compresson check and had no compresson in the number 1 and 2 cylinders so i took the valve covers off and found the valve springs were broken ( if you have one broken spring you should change them all because when i did it to mine alot of the other inner springs were broken also) well when that happened the lifter had come out of the hole and it lost oil pressure and took out the bearings, so out it came and i rebuilt it. It runs great now

[homefree]

The computer tells the injectors how much fuel the motor needs, on mine with the intake valve springs broken the valves would stay open into the cylinder and when the pistons came back up it would blow back into the intake and screw the computer up (basicly telling the motor hay i need more fuel and it just pours it in) You can change the valve springs with out pulling the heads off by putting a compressed air in to the cylinder thru the spark plug hole but you need a special hook up some compression tester have that option on them when you buy them.

[99ssconv]

sounds like you have a vacuum leak, make sure the throttle body base gasket is not sucked in, sometimes you can look down the throat of the throttle body and see if the gasket is deformed

[johnnymcbrown]

Today I replaced the (ignition spark regulator) and the 1989 truck 5.0L TBI, idles faster than ever. I reset the ECM and it slowed down some, but is still much to fast. Could a bad pressure regulator be the problem? Allowing to much fuel to spray into the TBI?

[homefree]

Jonny, read my posts i have the same truck that had the same trouble. Good Luck.

[johnnymcbrown]

homefree...
I read your post and I don't believe that's my problem cause..the truck runs and performs smooth as silk , no smoke, doesn't use oil, good running truck except "it idles very very fast about 2500 RPM

[johnnymcbrown]

I checked the temp sensors today and they are working. I replaced the Ignition Module, no help, replaced TBI gaskets, nothing helps the fast idle. I also checked the computer for codes, read 12 "all is OK" . I'm running out of things to replace!!!!

[troybuilt]

This is a trick re: the sensors and computer codes.
you can and probibly do have a few bad sensors that are loaded up but not physicly broken, thus the computer does not issue a code, it just re-adjust for a false reading.

[johnnymcbrown]

Which of the sensors, would be most likely to give a false reading to the computer causing "fast idle". Bear in mind I have replaced , 5 TBI sensors, ignition module, O2 sensor, already.