At my wits end with high idle issues.

[bigfutz]

Glad I found this thread. Thanks to the OP. I need to start at the top and absorb everything, so pardon me if I mention something that has been already answered.

I too have noticed when I have the high idle at start, it’s going to shift high and also not downshift on WOT. It’s like my TPS is not working but only occasionally. I ohmed my TPS through full travel - ohms out the same as a brand new one. It’s almost like occasionally it’s ignored.

Can someone please post a link to a OBD reader which works on my ‘95? I’m getting lost trying to shop for one and adapters for OBD2 readers and all that. Thanks in advance.

Now back to the top of the thread to soak it all in.

 

[PlayingWithTBI]

Can someone please post a link to a OBD reader which works on my ‘95?

There are options on posts 26 & 27 - look to see if you have a 12 or 16 pin ALDL connector...

 

[bigfutz]

Yes, along with TunerPro RT v5xxx software. This is a 12 pin ALDL cable, it'll work on 88 - 93. If you want to connect to a 94 or 95 you'll need a 16 pin.

http://aldlcable.com/aldl.asp

I have a ‘95 Tahoe Base and it’s got this 12-pin connector under the steering column. Is there another connector somewhere else I should be looking for?

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[PlayingWithTBI]

I have a ‘95 Tahoe Base and it’s got this 12-pin connector under the steering column. Is there another connector somewhere else I should be looking for?

Nope, that's it (12 pin) in 95 you should have pins A & M for coms where 88 - 91 used A & E. IIRC the ALDL cable I posted has E & M connected so it should work for all 88 - 95 years.

 

[Geoff Walliser]

Very interesting thread.

I have been reading over any and all high idle issue threads recently. My 92 C1500 350/5 speed has the dreaded high idle until it has ran for 20 minutes. Then it settles.

I have checked for vacuum everywhere, set base idle and timing. When I replaced the IAC I did the reset procedure. Unpluggged with it closed it'll idle perfect.

New O2, PCV, swapped the map sensor with a known good one.

The only funny thing I have come across is my brand new genuine GM TPS voltage reads .7 with key off. But reading this thread anything under 1 the ECM will read it at idle position. Is this correct?

When you push in the clutch and the idle surges up, in the A.m for my neighbors, it's so annoying.

LS Swap almost seems easier than fixing this at this point.

 

[Madscientist]

Just for ***** and giggles. Take a needle nose vice grips on the throttle blade stop bolt and turn it in a 1/4 turn and see if it changes anything.

 

[Frank Compagnon]

I had a similar issue a few years ago with a 93 blazer that I bought with a broke tranny. I replaced the tranny, tuned it up, got all the little bugs out of it, but it had an Idleing issue like is was hunting, I rebuild the TBI unit and was setting the IAC when I noticed the IAC pigtail had the holding clip broke on it and it could be plugged into the IAC motor a number of ways. I replaced it with a new one, everything was good.

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[PlayingWithTBI]

Take a needle nose vice grips on the throttle blade stop bolt and turn it in a 1/4 turn and see if it changes anything.

FYI the Throttle Body has a T-25 screw behind a plug for the min stop setting. This also shows how to calibrate your TPS too.

TBI tuning-website - Tuning the TBI.pdf

 

[Geoff Walliser]

I had a similar issue a few years ago with a 93 blazer that I bought with a broke tranny. I replaced the tranny, tuned it up, got all the little bugs out of it, but it had an Idleing issue like is was hunting, I rebuild the TBI unit and was setting the IAC when I noticed the IAC pigtail had the holding clip broke on it and it could be plugged into the IAC motor a number of ways. I replaced it with a new one, everything was good.

You must be registered for see images attach

I have replaced the IAC (I use all genuine parts) and it functions like it should when setting base idle etc. If it had the plug replaced and a lead was switched would that cause it to be lazy returning to idle? I have gone through everything else, I'm going to have to start checking for odd things like this.

I have also messed with the throttle body screw as a last resort, but unfortunately it still idles high for about 20 minutes, and takes forever to return to 600-800rpm idle which it eventually does. CTS was switched as well.

My 87 k5 blazer TBI high idles for about 30 seconds then come down nicely, I thought I could fix any TBI issue but this one has me stumped.

 

[PlayingWithTBI]

Put a scanner on it and watch your CTS, IAC, TPS, Timing, MAP, and O2 feedback. You may see something going on that shouldn't.