I've used the search function many times, lurked around alot and found alot of answers without having to post a question. My issues seems oppisite from others being that once the engine is warm it performs great with no problems.

However on a start up when the engine has been off for a while I get a slight surging from the engine, when i press the brake pedal it has a very noticable fluctuation up/down. I have checked for vacuum leaks and couldnt find any but it was a very once over check with carb cleaner. I'm thinking the brake booster or IAC.

1989 22RE

 

Unhook the vacuum line from the booster and plug it or take the check valve out and turn it around and see if the issue goes away. If it does, booster.

 

so i finally got around to try this and blocked the vacuum at the booster and its still doing it, anything else to try....

 

What's ur idle speed. Too high it'll do this. Also check ur timing.

 

the idle screw is bottomed and maybe 1/8 out. i'll check the timing tomorrow.

 

Hey your right down the road from me!

 

If your running the stock intake, check the elbow'd ends where it looks like a bellow for cracks. Definitley vacuum related.

 

Ok I'll check for cracks and go over the engine again for leaks. We're about 2 hrs away from my phone map. (Rockmart, Ga) I wonder why it only happens when it's cold though?

 

Not sure. Sometimes things totally unrelated affect other things!

Oh, I saw "the rock" we have a town 10 mins away called the rock. Cool.

 

vacuum leaks or holes in the intake pipes will cause our trucks to idle LOWER. high idle from vacuum leaks is a feature of MAP based speed density systems. MAF/AFM systems idle lower from unmetered air.

I thought my truck was vacuum leak free too (checked it multiple ways) but when I replaced the intake gaskets and injector seals it idled 500+ rpm higher than before. My idle screw is marked so I know I didn't move it during the work. the fixed vacuum leaks caused the idle to RISE from where it was (correct with the vacuum leaks)

If your idle speed screw is bottomed out and it's still idling too high, then someone adjusted the throttle to open wider. Probably due to previous owner stupidity and vacuum leaks

I really need to copy the 22RE idle lecture to a text file and reuse it...tired of retyping it . long story short, vacuum leaks cause more trouble at low throttle openings (greater % of total air) so at hot idle (IACV closed) the vacuum leaks are a major player causing low idle. so people open the bypass screw or throttle stop to bring up the warm idle to keep the engine from stalling. The problem is this additional idle air raises the cold idle too. when it's just started, the engine won't DFCO. After a minute or 2 of running, the idle is still up due to coolant temp. the normal opening plus the added opening from compensating for the vacuum leaks causes it to idle TOO high and DFCO cycle (the rpm hunting you notice). once it gets warm enough to idle under the limit of DFCO, no more surging.

 

You are down the road from me, I live in rome, seems we are getting more and more members in NW GA!!

 

Good post. I just replaced my HG and it was idling high. Idle screw all the way in. Decided to use duct tape so it wouldn't suck in the engine since it sticks well, an covered up the inlet for the IAC. Fired it up and booyah. Low and smooth. So I removed the throttle body, took the IAC off, and the rear plate where the thermovalve unit is and set that in a pot of boiling water. Sure enough the valve wasn't closing. Easy fix. Turn the part the IAC closes against to seal the air in a lil further, seal everything up, reinstall and booyah again. 750 smooth.

Also adjusted the TPS while I had the throttle body off. So , I guess it just needed it lol. So it's good to go.