P0122 indicates low voltage... there could be a poor crimp connection in the TPS harness connector between one of the wires and a terminal. Can you watch TPS voltage, (key on, engine off) with a scan tool or a DVOM? The TPS and or IAC motor could be causing the idle issue. You can try spraying some carb cleaner around the plenum & intake gaskets while the engine is running, if it smoothes out/changes speed, look close for a leak. You can also try kinking the power brake booster vacuum line and see if that makes a difference.

 

I tested the TPS before, and it was 4.5 volts or something at closed, or WOT or whatever it was supposed to be. I knew at the time. The IAC is like $150, I'd just replace it otherwise... Will look carefully for leaks though...

Is there a good way to test the IAC? Will try kinking the brake booster line too, it occurs to me the brakes are irregular in function... Maybe a bad booster...

One more piece of information that may help, if you crank the engine over, it will usually start and run momentarily (1-2 seconds) then die...


Thanks!

 

3 wires at the TPS:
With the TPS disconnected, measure at the harness connector:
Black wire should show less than 5 ohms resistance to ground.
With key on, engine off, grey wire should show ~ 5VDC
Reconnect the TPS.
With key on, engine off, Dark blue wire should show ~ .6VDC at idle and ~ 5VDC at WOT.

 

Well, checked for vacuum leaks... Nothing. Not the brake booster. Will test the TPS again based on your post and see...

 

Tested the TPS...

.69 VDC @ closed throttle

4.61 VDC @ wide open throttle...

Is there any way to test the IAC?

 

Checking the function of the IAC requires a bi-directional scan tool capable of accessing it, (not your everyday DIY scan tool). Once you "dial in" to the IAC you can command it to change RPM. Bi-directional scan tools are not cheap so you might want to have reputable shop check it out for you rather than replace the IAC, possibly needlessly.

 

Ok... Thought it may come to that... I'll see if I can find somebody with said scan tool and see what turns up...

Thanks for all the help, and I'll be sure to let you all know what it turns out to be.

 

An experienced technician with the right test equipment, should be able to spot the problem rather quickly just by looking at all of the data streams.

 

Found a shop that has a big scanner... He said he'd have time at the end of the wek to look at it... $45 which seems reasonable I guess.

In the meantime, I moved the blazer saturday because I wanted to work on my '87...

the blazer is backfiring and has code P0300 (Random Misfire)

But it idles on it own for the first time since I bought it!

I'm really stumped now... Thinking maybe the timing chain is bad and jumped a tooth... that could possibly explain everything...


The other thing I noticed, since I could get out of it while it was running for the first time, was the amount of moisture coming out of the exhaust... it really puts out alot of water... But it has absoloutly no smell of antifreeze... granted it is cold here, but it's way worse than my 98 suburban...
Thoughts? I'm not sure I could even drive it across town to the shop in the shape it's in now...

Look foward to your sugestions... (Aside from "Why did you buy it", which I've already thought of lol)

 

I service several 4.3's in a fleet, some of them have upwards of 300K miles, never had an issue with a timing chain. IF the chain were to jump, P1345 would be set in memory and the SES light will come on. The P0300 is almost always caused by a fault in secondary ignition; spark plugs, plug wires, cap, rotor and coil. Worn distributor shaft bushings along with low fuel pressure can also cause it.