7 replies to this topic

[Mike Van Eepoel]

During my last session I noticed that the car seemed to be lunging under full throttle. It would lose power, then gain power, then lose power off and on at the end of the race. It kept running, it just seemed to "surge". While loading the car on the trailer and unloading at home, the car revs up to 2K then down to almost cutting out, just to rev back to 2K again. It revs up and down continuously without me even touching the car. I have checked the ground cables, plug wires, and sensor plugs. I'm sitting on about 1/4 tank of fuel. I have no idea what would cause this. Has anyone experienced this? What could be the cause, I'm stumped.

[Dirt Surfer]

Sounds like a vacuum leak to me did you check the accordian part of the tube running form the Throttle body to the AFM? They will spilt in the ribs sometime.

[Jaime Florence]

I just had this same type of thing happening on one of my cars. It turned out to be the butterfly flappy thing inside the throttle body. One of the small bolts had broken and the throttle plate (flappy thing) was moving around inside the throttle body causing spazzy idle and I'm sure other issues.

If you find that your issue is a broken throttle body, be sure to check to make sure that your throttle pedal isn't yanking the throttle cable beyond 100% open. I believe this is a major cause of throttle body breakage.

I hope this helps.

Jaime

[DES4]

It's most likely unmetered air entering the motor somewhere. As above, vacuum leaks are the most common cause; check hoses, brake booster (does brake application affect it?), injector seals... any possible point air might be entering. Spraying carb/brake cleaner around suspect areas can help; listen for drops or jumps in engine speed while hitting said areas with spray. Also, the induction hose that leads between the MAF sensor to the throttle body (as stated above) can cause erratic idle issues if air is bypassing the MAF (cracks/splits/loose connections). Pulling up codes can help; MAF faults are normally a good indicator of a leak, and although a failed MAF is also a possibility, it is less likely.

[Mike Van Eepoel]

This all make some sense, although I did not notice anything vacuum lines that had popped off, or loose hoses. I will do a thorough search from air box to TB and see what I can find. I appreciate everyone's help!

[Mike Van Eepoel]

I wanted follow up with the outcome of the issue I had, just in case someone else has these experiences the same thing. After checking the diagnostic codes, which I should have done to start with, I got a 25 (25 PRC solenoid valve) followed by a 9 (09 Engine coolant temperature sensor). Both of these monitor and adjust fuel pressure. I replaced both and now have a smooth idle @ 900 RPM. Looking forward to Daytona in May,

[Danny Steyn]

PS Mike

LOVE your signature!!!

[LarryKing]

Neat trick