Idle Pulsing - what could cause this?

[HartmanMS]

My Talon has been idling poorly for a few days now. It sounds like a V-8 with a big cam. It is like an idle “pulse”. The idle sometimes pulses around 650-850, and sometimes around 900-1000 rpm. When I first start the car, the idle starts high, like normal, at about 1500, dropping down and pulsing a second or two later, with a vacuum of about 8-10mm/Hg. If the car is in gear decelerating, the vacuum drops to 17-18 mm/Hg. This is where the vacuum used to be at idle. I thought it might be a bad EGR, so I blocked it off. I also removed the emissions parts and left all of the solenoids plugged in and capped the ports on the TB. I did this process according to Taboo Speed Shop’s directions. I also checked for vacuum leaks. I was wondering what could cause this odd idle problem. Any ideas? Thanks.

P.S. The car runs pretty rich, but it was running rich before I had this problem...

 

[HartmanMS]

Well, not knowing what else to try, I made a grounding cable to ensure the ground of the TB/IM to body. This did not help. My exhaust isn't grounded very well (a cut up clothes-hanger), but I dont think that would cause this problem. I guess I am going to have to break down and open my wallet...I will take my Talon to Lambeth Auto on Monday, they are a pretty good (albeit pricey) shop. I will have a smooth running 13 second Talon again soon. Who wants to give me $6500 for her when shes done, ? I'll repost on this thread when I get a diagnosis/fix. Thanks for the attempts at fixin the car, guys!

 

[HartmanMS]

Well, today before heading out to go see a movie, I had a half hour or so, so I was going to try some things on the Talon. I pulled off my vacuum caps on the TB, and blew some carb cleaner in there. I recapped them, and turned the car off after a minute or so. Then, I pulled my MAF, and cleaned the inside out with a clean cloth, and blew it out (it would be nice to have some Electrical Cleaner...) Then I took her for a spirited drive, and to my pleasant surprise, the idle is now only minorly fluctuating about 50 rpms(from about 1295-1345 on the logger). The timing is now stabilized to fluctuate from about 15-19 degrees advance at idle, which I think is a bit high, but so is my idle, I will decrease idle later. This is much better than the 200 rpm fluctuations and timing fluctuations of 4-20 degrees before. I might pull the isc and clean it later also.

 

[johnk]

I've never heard of the coolant temp sensor making idle surge but it can cause you to run very rich.