driveability issues at lower RPM's....idle issue?

[svasica]

When I rev up the engine the idle will lag before coming all the way down to its idle of about 900. This presents driveability issues when I'm driving at lower RPM's from 1200 to about 1800 and also when letting off the gas because the engine sorta wants to "push" the car instead of braking like it should.....it basically starts bucking and jerking and gets into that cycle until I apply some more gas and get the RPM's up. I've heard this can possibly be a IAB issue? Some have said I have to take apart the IAB and modify it?

I'm running an IAB plate. Also, the 10 pin connectors on my car had those extensions (I think it was part of a recall or TSB that Ford had back in the 90's) but I heard that they were useless so I took them off. The IAB plate and EGR are new and clean.

The idle is basically fine otherwise, its just this pesky annoying lag that is a driveability issue at lower RPMs (not to mention when I rev it up at idle it doesn't come down to the idle right away and sounds stupid).

 

[Raginstang]

Hey, I had this problem after I installed a new throttle body. I found that I needed to back off the idle stop screw under the throttle body. this adjusts the throttle blade. I would adjust the blade or back the screw off so it closes the throttle blade more, then adjust the TPS. you may be experiencing a bad of missadjusted tps also. get back to us. I thing the tps should be around .98 to 1.0 or something like that.

 

[HISSIN50]

Agreed. It sounds like you have a vac leak.

 

[svasica]

I set the TPS voltage to about .98-1.00. Also, no matter where the final idle is, the car will always lag before coming down to that final RPM (I've tried several different idle RPMs by backing off the idle screw).

 

[svasica]

TTT

 

[HISSIN50]

Did you find any vacuum leaks? What kind of manifold vac reading are you getting (if you happen to have a gauge around to check with)?

Good luck.

 

[KENS89LX]

Try wd-40 on the throttle body spring located under the throttle body i have to do that on mine. It cured my symptoms similar to yours.

 

[svasica]

I'm getting a vacuum reading of about 10psi at idle. The throttle blade returns to the set screw once i let off the gas pedal, i don't believe the spring is the problem. Im guessing its some sort of computer/electrical/vacuum issue, probably not mechanical in the sense that the TB doesn't close all the way.

 

[jrichker]

I'm getting a vacuum reading of about 10psi at idle. The throttle blade returns to the set screw once i let off the gas pedal, i don't believe the spring is the problem. Im guessing its some sort of computer/electrical/vacuum issue, probably not mechanical in the sense that the TB doesn't close all the way.

The 10" of vacuum is a bit low. As Hissin50 advised, look for a vacuum leak.