1995 CPI Erratic Idle AGAIN!

This is REALLY starting to friggin piss me off.

The truck runs fine most of the time but sometimes it won't idle properly. It's a crap's shoot whether it will run fine.

This is what has been replaced:

IAC Valve
New CPI and Nut Kit
Cap & Rotor 10,000 miles ago along with a new fuel filter.
New Pre & Post Cat O2 sensors 1000miles ago.

I am getting no codes whatsoever.

I start it up and take it for a drive and find that when I put it in park the idle is hunting between 800-950rpms randomly up and down, not pattern or rythym. Get this, I turn the truck off completely for 3 seconds, start it up and it will idle down perfectly and purr at 750rpms steady.

Now I tap the throttle every so lightly and give it a rev to 1300rpms and the idle will go down to 850-900rpms and will kind of stick there and not come down to 750rpms idle where it should be. Again, I turn it off for 3 seconds, fire it up and it idles like a friggin dream,,,,,, ****!

So I start it up again and go over to the OBDII computer mounted on the passenger wheel well on my 1995 BlazerLT and I start wiggling every electrical connector in sight starting from all the visible sensors and making my way back to the actual computer itself.

Everything seemed to unaffected by moving the connection and making sure they were all the way in until I eached the actual computer itself. When I grabbed the "BLACK" labeled connector going to the computer and firmly pushed it in place while wiglling it up and down, the engine idle all of a sudden starting going slightly erratic again and slightly hunting for the idle. I continued wiggling it until it leveled out at a higher rpm. I then went to every other connector on the computer and made sure that they were seated firmly.

I went around, jumped in the driver's seat and turned the engine off and them started it back up again. Engine reved normally, then settled to 850, 800, 750rpms and remained completely stable.

I punched the throttle up to 1400rpms and the idle settled back down to 750rpms.

This is weird, what did I do? The computer connectors seemed a little loose but there were in their clips.

Should I remove the connections and look for rust and maybe use some dielectric grease or something?

Anyone have some input on this?

lol, did I stump you guys?

Your a pretty smart guy BlazerLT and you have a lot a good info you impart here but let's look at this from an electronics point of view. I'm sure what I say you will more than likely say "oh crap, that's right" but here goes. Even though the connectors are weather proofed (haha) minor humidity still gets in there. This will cause an oxidation on the connectors that is sometimes not visible. Your moving them simply caused the connector to clean itself. Will it last? who knows. What I have done is this, I have a set of burnishing tools that I use to clean both the female and the male. If I don't have the proper tool, I have used CRC 2-56? (have to look at the can again). It works great. I would clean the connections and put the dielectric grease around the weatherproof portion of the connector to act as a barrier. Sounds to me like you traced the problem very good instead of shotgunning and changing too many parts. I'm sure I would have done the same since I have only ever had a connector problem at the ECM only once. That too drove me nuts. Good Job!

Thanks for the kind words.

I just took the truck out for a nice drive around the city and it works great.

Idle is smooth as silk at about 725rpms, and there is no hunting anymore.

I have some contact and head cleaner here and I think I will remove all the connectors and give them a good spray and dry them out.

I forgot to say I also replaced an alternator thinking that is was weak and indeed it was and had a whining bearing, but it was not causing the hunting idle problem.

What made me think this, well, I have a 800watt stereo in my truck and I found that the truck would run like shit if I would run the stereo for a while. Turns out that made the vibration of the subwoofers kicking was causing the connection to not be in contact due to vibration.

I will keep you updated as I monitor this over the next week. Since wiggling and reseating the connectors, the truck has never been better and even has a little more pickup.

I think I need to clean the ECM ground.