Last weekend I had a DE event where I had an off-track excursion into the dirt. I managed to get back on the track for six more laps when all of a sudden I loss power. The car crawled back into the paddock with the idle fluctuating without being stable.

I noticed that intermittently the idle would hold when placing pressure on certain hoses however after sometime, the idle would oscillate again. My first assumption is that one of these hoses has a leak in them BUT would a small leak cause this amount of pressure to be lost where the car is not drivable? I would think that the characteristic of my problem is due to a larger leak.

The car was trailered back home where I found that the vacuum line going to the wastegate was severed. I repaired the line however, the idle is still fluctuating. I checked all the intercooler couplings, replaced the vacuum lines but nada. What other components can be checked to see if they are functioning which will have the same affect?

Thanx

 

do you have an aftermarket boost gauge on the car? What is your Vac. reading at idle and when warm.

 

+1 for a boost/vac gauge, very helpful in diagnostics. Try resetting the idle using the factory procedure.

 

What should the vacuum reading be at idle? Mine seems low to me.

 

Most of our cars on cold start will be around 17-18 in/merc and will climb up (down?) to 19-20 once warm.

 

ok..so my diverter valve was shot so I picked up a new one. The problem is at WOT, when I depress the pedal to floor the idle fluctuates.

 

UPDATE: with TPS disconnected WOT is constant but as soon as I reconnect the plug, WOT starts to fluctuate. I did not hear any clicking at the TPS and decided to open it up and found that the microswitch plunger is broken.

What affect will running without a TPS connected cause?

 

WOT at redline? WOT has nothing to do with idle really. At WOT, you will redline within matter of a second and its supposed to fluctuate as the rev limiter kicks in.

 

yeah is it WOT or idle? Idle is when you are not touching the gas at all. Sounds like you need to pull the intake and start checking for broken hoses..

 

FWIW I drove with my TPS unplugged for a few weeks with no issues. It runs a bit richer, but runs ok.

 

So to clarify my situation. With the car parked, when I to depress the gas pedal, it fluctuates where the RPM gauge goes up and down. The gas pedal doesn't have to be depressed all the way down, even partially when the engine oscillates.

 

if it does not click, and with it unplugged it runs better you have a bad TPS.

 

UPDATE: replaced TPS with a known good one from a friend and still the same issue. What is weird is that when disconnect the TPS the car run fine and even has boost.

 

UPDATE: replaced TPS with a known good one from a friend and still the same issue. What is weird is that when I disconnect the TPS, the car runs fine and even has boost @ 10 psi. When I reconnect the TPS and partially depress the gas pedal (1/2 way down), it fluctuates up and down....any other ideas?

 

I would say that now it's time to start tracing some wiring. You have narrowed it down to the TPS circuit. There are methods for testing the wiring harness that require usage of a multi-meter and a lot of patience/time and a friend. If you need any diagrams let me know.