Here's a quick update to my ongoing idle problem on my 86 S10 Blazer 2.8L.

So far I have;
-Changed the IAC - no effect
-Found the EGR solenoid is toast - unhooked EGR vacum, idles more smothly, when it does.
-Changed TPS sensor - no effect
-Changed Coolant Sensor - no effect
-Checked all connection at ECM and made sure it was grounded - no effect

Tonight I hooked up a Volt meter to the O2 sensor. The sensor works fine. Under light throttle it is usually 0.30-0.50V. Give it gas it goes up to 0.70V.

Here's what was happening tonight. Afew times when I stopped it would idle fine ~700rpm, O2 was about 0.60V. When I stopped and the idle speed went way down ~500rpm O2 would jump up to 0.80-0.90V. When I got home, I put the truck in park idle jumped up tp 2000rpm and O2 went to 0.01V. After about 1min it came back down and O2 went to 0.60V. Touched gas idle went high for 30sec and came back down. I shut truck off, and turned key to IGN for 30 seconds, restarted it and idle was way high at 2000rpm, O2 at 0.00V again. I drove the truck around alittle, when I touched gas O2 would go to 0.30V-0.50V. When I let off O2 dropped to 0.01V. Idle speed would not drop back down from 2000rpm.

That's how I left it. I 'll see what happens in the morning after it has been sitting all night. Before the only time it would idle real high is when the TPS was set below 0.37V. That's where it I reset it, so tommorrow I will some different settings and see what happens.

Thank You for any help
Steve

 

Man... i wouldnt drive it like that untill you find out whats going on. It could be a bad ECM. I had a similar problem after my cam swap. I started the car after it sat for a couple of weeks and it did something very similar. Luckely i had winALDL capturing data so i knew what happened afterwards. After break in, the idle was reaal high and the O2 volts being regisered just kept going down untill eventuially there was no output at all and the engine began to detonate and the headers where glowing bright red. For some reason the ecm jsut wouldnt correct for the lack of fuel. It jsut locked at 128 int/blm even though it was in closed loop. I got back just in time to hear the engine detonating real bad and there was smoke coming off of everything. I reset the ECM and its been fine ever since. Hopefully (knock on wood), it didnt do any perminant damage. Doesnt seem to have done anything perminent but it sure was scary. If the fuel press looks ok and there are no apperent vacuum leaks, Id take the truck out to the dealer to have it checked out.

 

As dimented24x7 said, reset the ECM

If your troubleshooting shows your EGR is bad, get it fixed. That may be your whole problem.

Check for vacuum leaks. You can temporarilly block off vacuum lines one at a time to check each system (dont disconnect your map sensor)... watch your idle while you do this. The power brake setup can be a major cause of leaks. If you dont find any there get a can of carb cleaner and spray at all of your intake / throttle body gasket surfaces. A rise in rpm will also indicate a vacuum leak.

Use your multi-meter to check your map sensor. One wire is ground, one a 5 volt reference and one is the 0-5 volt signal to the ECM. Take your readings from the ground/signal wires. The values should fluctuate with throttle position. Inspect the map vacuum line for leaks or kinks, etc. Monitor your TPS also... is it at the correct throttle closed voltage? Does it fluctuate up to nearly 5 volts fully open?

 

Well it doesn't matter anymore. Motor is dead. Sounds like a rod bearing. The motor was already in rough shape, and I knew it would blow up sooner or later.

This summer it's getting a 350 so I don't want to spend anything on the 2.8L. I have a few more vehicles I can drive so it's no big lose.

Thanks for all the Help
Steve