Hi guys,

Forgive me if this is in the wrong spot. I have a 96 blazer 2 door that I have been having problems with. Many of which I have gotten through from previous experience and help from this forum.

Yesterday on my way home I had the high idle, not wanting to slow down issue. I checked for vac leaks with both propane and carb cleaner. It sounds like the brake booster has an internal leak that might be causeing the vac leak (if there is one).

A little history on what has recently been replaced that I refered to earlier - cat (P0420), muffler (clogged from cat), tail pipe, driverside o2 (was reading lazy),brake switch, vss, tps, temp sensor, mfi conversion ( leaking gas from regulator, decided to replace it all while I was in there), distributor (used original sensor, gear was worn, I have not had a chance to get the stealership for relearn yet as I work 6 days a week), map sensor (found to be bad last night using manual vac pump, dipped down to .01 volts with 10 psi applied, 5.04 with no vac applied).


So on to my question, will a vac leak in the brake booster give a false bad iac result? I have the $129.99 actron scanner so i have , maf, map and tps readings if that will help.


Thanks,
Don

 

A leaking booster could be a rather large vacuum leak. To see if the booster is leaking, run the engine, then shut it down and wait a little. After a minute or so, pull the check valve from the front of the booster. If you hear a rush of air into the booster, then the check valve and booster are holding properly. If not, you could have either a leaking booster or a bad check valve. To test the check valve, run the engine again, shut it down, and quickly disconnect the booster vacuum line from the fitting on the lower intake manifold. Put the end of the line to your ear and listen for a leak.

If you haven't done so already, you should probably clean the IAC valve and bore to make sure that it isn't just sticking.

 

Thanks for reply, Kyle I believe i read in another thread. I didn't have my test light with me at work so I couldn't follow your diagnostic for the iac. I cleaned the egr, maf and iac last monday. The egr and it's passage ways through the lower manifold were pretty clean for having 178,000 miles.

The iac was pretty dirty though. I did a visual on my lunch break to see if it did slide though. Not sure if this really verifies functionality though. I disconnected the maf, removed the intake tube and started the truck. I played with the throttle to simulate light acceleration and it slide back and the reseated itself when I let off.

I also verified the voltage comage to and from the tps thinking maybe I got a bad sensor. It read 5.01 v. in ( plug disconnected), .61 v. at idle, and 4.87 v. at wot. Which I believe I read yesterday on here was with specs.

Pulling the check valve out of the brake booster should good, the only reason I was thinking it might be going bad and be the cause of my problem is the pedal sighs, for a lack of better term, and seems to be louder than it has been for the engine bay side as well(ear hold to the body of the booster). So I was thinking maybe the diaphram is getting weak.

I do have another question for you though. Last night I noticed a two week old acdelco pcv valve was not fluttering at all. So tonight on the way home I stopped by Advance and picked the cheap one along with some replacement boots as the ones on there were getting dried out. I swapped out the valve and noticed a slight difference on the way home.

When I got home I swapped the boots and it got better but still not perfect. My idle is fluctuating a little and at times holding around 900 rpm. This coming weekend I plan on crawling around cleaning some grounds up. Any ideas beyond this?

Sorry for being so long winded on this post.

 

The throttle is closing all the way, right?

 

Yes sir, throttle plate is closed all the way. The bevel underneath is still there. The hole in the plate is clear, I was able to stall it by covering the slot for the iac with my thumb which I would expect. I even checked the the set screw to make sure the plate was not being opened by it at all.