What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

High Idle on TBI

jeff in co

jeff in co

1/2 ton status
 Premium
Joined
Nov 14, 2003
Posts
2,198
Reaction score
446
Location
Colorado Springs
I've been replacing a few parts here and there but have now noticed a high idle when the truck is cold and warm.

I've replaced the EGR valve, new injectors, new vacuum lines and new IAC valve.

I also checked the throttle positioning with a multimeter and appears to be working correctly.

 After installing the IAC valve, I went through the following:

Jump the A and B terminal in the ALDL connector then turn the ignition to the on position (do not start engine) and wait for 30 seconds then disconnect the IAC wiring connector and then remove the A/B jumper and start the engine and adjust base idle. Once adjusted shut the engine off and reconnect the IAC wiring.

When I get to the "adjust base idle" portion, the engine sounds great and the idle is down to about 700rpms. So, I didn't touch the adjuster screw....however, I did notice the screw cover was gone so someone has been there before.

After complete, it sounded great and the idle was much lower now. I turned it on a few times and still low rpms. I was thinking, great, it's fixed!

But about 5 minutes later, I came out and started again....now back up to 1100 rpms.:confused:

Observations:
Just before I unhooked the IAC valve connector, I heard it clicking pretty good. Would this be normal?
When I installed the new IAC valve, the overall length of the unit that goes "inside the tbi" was shorter than the one I pulled out. The instructions talked about it not wanted to be too LONG but nothing about too SHORT.

I have not replaced the tbi gasket yet but will. I just don't know why it would be perfect for a few minutes and a few key cycles but then 5 minutes later, rpm back up.:dunno:

Any help would be greatly appreciated.....
 
Mine did that high idle recently but it was right after I installed a new IAC valve. It ran high idle even after warming up. After I shut it off I started it up again a couple of times and the idle came down to normal. I think it takes a few starts for the new IAC valve to extend and seat properly. Just to be safe I cleared all codes and it hasn't happened again.

I was told whenever you remove the IAC valve, always press the plunger back into it before reinstalling into the TBI. The new one was probably already depressed and that's why it was so short.
 
Mine would intermittently have a high idle, the linkage had gotten a little sticky causing the blades not to close completely. I thought is was a bad IAC at first, but the problem stayed after replacing it (for the third time, it was actually bad the other times). I then found that manually pushing the linkage closed would settle down the idle, even though it felt like it didn't move any further closed.
 
Jeff
Yours is a also an 89 and you should not have to set the minimum air. You may still have a small vaccum leak at EGR, IAC or TBI base. Check to see if your throttle cable is holding the TBI open as well. This was my most recent issue. I had to remove the cable and bend the bracket forward abit to solve that problem. It was either that or remove my TBI spacer and i want the spacer there. Start the truck with the cable off and with the truck running try closing the plates by pulling them shut with your hand.
 
Base idle (with the iac disconnected) should be set at 550rpm, 700 is too high. Also, check for vaccum leaks.
 
07coupegt said:
Base idle (with the iac disconnected) should be set at 550rpm, 700 is too high. Also, check for vaccum leaks.
Click to expand...

OK, here is what I've done today.....

I did replace the tbi gasket and noticed that the old one still was in good shape but I went ahead and changed it anyways. I also threw on a new pcv valve for good measure.

I disconnected the battery for 30 seconds and then went through the whole "re-setting" process mentioned in my original post. Although I was kinda going by memory on the rpms before, I paid a bit more attention this time.

when I disconnected the iac unit, the rpms actually hovered around 500 to 550, as-is. So I didn't touch the idle screw. I shut it down and reconnected the iac. Started it up and it sat at 550 or 600. I let it idle for a few minutes and then turned it off. Re-started......rpm went back up to 1,000 rpms. :mad1:

So, still there basically.

I did also test the MAP sensor today and noticed that I did get the full 5V as described but when I tested the other terminals, I got about 3.5V rather than the suggested 0.5V.

It did say that the 0.5V would be close to sea level but I wouldn't think that 3.5V was "close to this" considering my elevation of 6500 ft.

So, could the MAP sensor be part of my problem??
 
Problem with Stalling- Similar issue

In my 89 TBI 350 I can drive beautiful for 30 minutes, then after a few stop and goes, the idle drops and it almost stalls- then the idle goes high, drops low then stalls. There was a trouble code 32 and code 42- EGR and Timing ignition. This was after it first happened. I then changed the Ignition module, problem came back after 35 minues of driving. Then I changed the TPS sesor (throttle position sensor). It came back. Then I changed the EGR valve. Now the problem still happens after the truck runs for 30-45 minutes in stop and go traffic, then will idle rough and stall. Each time the truck starts back up but now there is no trouble codes that come on after the last two times it happened. Now wwhat?

Here is another thing- the previous owner had the EGR vacuum line hooked up to the VENT nipple on the EGR sensor instead of the nipple below it. I'm thinking it may have messed up the EGR sensor? A ASE Certified mechanic said it may be the distributor pick up coil or something with the ignition.

I keep shooting in the dark and so far I have changed the EGR, TPS sensor and ignition module and the problem is still there. But now no trouble codes the last two times it happened. Please give me some advice. Anyone know the proper method for testing the distributor and/ or the EGR solenoid. Any ideas on the problem? The truck only has 77k original miles and runs 100% otherwise.
 
Like you I changed all of my sensors when I was having this issue of running rich, code 32 and stumbling at lights etc. After all that it was a busted EGR that was the culprit. I dont know a way to test the solenoid but I do know its about $15.00 at Advance Auto. Also, a sticking throttle cable was contributing to my high idle as it prevented the plates from closing. It does sound like the EGR is the caused as pointed out by a few experienced members on here, "most stumbling issues can be attributed to it" but check out all the other sensors too. You can pull the distributer module from beneath the cap and have it tested at the local Autozone.

Blue Stomper said:
In my 89 TBI 350 I can drive beautiful for 30 minutes, then after a few stop and goes, the idle drops and it almost stalls- then the idle goes high, drops low then stalls. There was a trouble code 32 and code 42- EGR and Timing ignition. This was after it first happened. I then changed the Ignition module, problem came back after 35 minues of driving. Then I changed the TPS sesor (throttle position sensor). It came back. Then I changed the EGR valve. Now the problem still happens after the truck runs for 30-45 minutes in stop and go traffic, then will idle rough and stall. Each time the truck starts back up but now there is no trouble codes that come on after the last two times it happened. Now wwhat?

Here is another thing- the previous owner had the EGR vacuum line hooked up to the VENT nipple on the EGR sensor instead of the nipple below it. I'm thinking it may have messed up the EGR sensor? A ASE Certified mechanic said it may be the distributor pick up coil or something with the ignition.

I keep shooting in the dark and so far I have changed the EGR, TPS sensor and ignition module and the problem is still there. But now no trouble codes the last two times it happened. Please give me some advice. Anyone know the proper method for testing the distributor and/ or the EGR solenoid. Any ideas on the problem? The truck only has 77k original miles and runs 100% otherwise.
Click to expand...
 
I had to replace my TBI unit because the throttle shaft bushings were toast and the blades would not close all the way. PO tried to fix this by adding a throttle return spring. All he accomplished was making the pedal rock hard and the idle was still too high...
 
I went to the junk yard yesterday and picked up a "new" map sensor out of a 91 suburban for $8. I swapped it out and then went through the whole "re-setting" process.

Unfortunately.....still there! I've checked for vacuum leaks and can't seem to find anything. I checked the linkage and tried to pull it "more closed" but nothing. It's as close as can be.

I guess it makes sense to try and fabricate an OBD I cable and see if I can determine anything from the laptop approach.

On a good note, I got the cruise to work and swapped out the 37" tires for 35" BFG Muds ($400 - 80% life).....looks much better now!
 
I seem to have figured out the issue- how about this for weird- the rotor was rubbing up against the cap- making misfire when hot and setting the code 32. The small end of the shaft seems to have a 1/32 of an inch up and down play. I sanded the top of the rotor slightly and no more problem- I will need to change the distributor eventually i guess though.
 
had same problem in my old 87 - first year TBI..

finally tracked it down to the fuel injectors...the o-ring at the base had bulged out of place, causing raw fuel to dribble into the throttle body. Kept getting a code 32, iirc..(egr code)

I didn't know anything about fuel injection at the time, so I kept adjusting the throttle stop screw...:whistle::doah::haha:
 
okay- I ate my words- I left my 88tbi idling for about 15 minutes today and it started to stumble. I turned it off, then started fine, then stalled twice at red lights, then drove decent on the highway ride home. The code 42 came on again- Im thinking this is the time to change the distributor. Jegs has one for 350 TBI chevy truck for $120. What do you guys think?
 
Code 42 again- on and off

Blue Stomper said:
code 42 again?
Click to expand...


i dont get it- the truck seems to run fine...but every once in a while when driving in stop and go traffic the idle will drop, then acceleration will drop like it stalling then code 42. If i restart again its fine. It is something with the EST- I already replaced the whole distributor and doing a cap/rotor and module change. Where is the EST? Any ideas?
 
Blue Stomper said:
i dont get it- the truck seems to run fine...but every once in a while when driving in stop and go traffic the idle will drop, then acceleration will drop like it stalling then code 42. If i restart again its fine. It is something with the EST- I already replaced the whole distributor and doing a cap/rotor and module change. Where is the EST? Any ideas?
Click to expand...

Did you get anywhere with this one yet?
 
You must log in or register to reply here.

Latest Posts

Top Bottom