Well. After installing the new engine in Sept, I had a slight idleing issue. The car would not find a happy median.. it would go up and down about 100-250 rpm's in park and neutral. After a couple months it would make me wait a minute until the car warmed up.. or it would just die. After a 5-10 min of driving it would idle better. After much research and tests, we found the brake booster to have a slight leak in it which got worse with time and caused a vacum leak which caused the low idle and unsteady idle. We repleaced the IAC motor, the brake booster, reset the minimum idle and everything was back to normal. Start it and it would shoot up to 850-1000 in open loop, go to closed loop and have a nice 650 idle. In gear would idle around 550-650.

Well.. a couple weeks later.. out of the blue.. it is idleing way low. Start it up and its only at like 500-650.. put it in gear and it is at like 300-400.. steady and not completely dieing, but wanting to. With a little throttle it will pick up and go.. but at any stop light or anything it will idle really low and barely stay alive. Sometimes will almost die. Hasn't died on me yet.

So i got and get a piece of vacum hose and cut it just enogh to stick it over the tb adjustment screw so that it won't let the car idle that low. Won't let the tb blades close enough. So its idleing at like 1200 in park and neutral and 650 or so in gear. Well.. i get sick of this and decide to take it off and reset the computer. I do this and i get it back to how it was when fixed. All is working fine.

2-3 days later.. i start it up and its back to low. So i put the adjustment back on to keep the tb blades from closing as much and its still only idleing 550 or so in gear.. 750 or so in park and neutral. Does this for a day.. then the next day it starts up and idles back to 1200 or so and then 650 or so in gear.

I am so confused. I would think if there was a vacum leak it would be a consistant issue.

I am curious if the fuel pump is doing its job. I am just so lost.

 

any ideas?

 

What are your IAC counts at idle warm and your TPS voltage?

 

Have you tried to pull any engine ECM codes?

It's possible you still have a vacuum leak, possible on the TPI runners or plenum. Check to make sure everything is still bolted on tight (throttle body, runners, plenum, etc.). Could be that it takes warming up and expanding for the leak to start. Kind of strange though that it worked for a couple fo weeks before acting upa gain... was there a significant warming period over those 2 weeks?

Other than that, I'd check vacuum lines under the hood. Could be that you've been under there for something else and moved an old weathered line so that it started leaking again?

This is definitely a strange one, for sure. I'll get back to you if I think of anything else. Check all your sensor electrical connections as well. My old 305 acted pretty strange like this for a while, ended up being the EGR valve was plugging up, so I replaced it and cleaned all the carbon out of the plenum and runners.

Good Luck!


- Vern

 

actually since its an automatic check the transmission kickdown cable hooked up to throttle linkage
cable could be binding or misadjusted
let me know if it helps, would like to know if im right lol

tim