Idle & boost issues; HELP!!!! Losing Sanity:
04-05-2005, 11:51 AM
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Racer
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Join Date: Sep 2004
Location: Farmington, MI
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Idle & boost issues; HELP!!!! Losing Sanity:
On an '89 951 w/ 42K miles, with Milledge Engineering chip "kit" (chips, shimmed WG and drilled Cycling Valve?:
Upon cold start or restart (within 30-60 minutes) the car will hunt for an idle. When the idle stabilizes a bit and I put a load on the car by driving away the car will stumble, hesitate and occasionaly burp out some black smoke.
The car had/has new Magnecor 8.5mm wires when the issue developed.
My shop has gone through the known suspects:
Smoke test for vacuum leaks shows only a small/"normal" leakage @ Idle Cont. Valve
Replaced Engine Coolant Temp Sensor
Turbo Bypass Valve checks as normal
New O2 Sensor
Replaced Throttle Position Sensor
Plugs replaced
Cap and Rotor replaced
Coil replaced
Scope pattern on Air Flow Meter (MAF) checks as normal
(Primary) Fuel Pressure Regulator replaced
Swapped out Milledge chips for OEM and vice-versa
Monitored the (Motronic?) data stream
Still no joy. Rough/fluctuating idle begins a few seconds after start-up , hesitation and stumbling under initial load still evident. Shop says that they theorize that the root cause of the issue is probably being masked when warmed up as the O2 sensor does its' job.
Next steps for the shop is/are to attempt to isolate the operation of the Idle Control/Stabilizer Valve and the operation or contribution to the symptoms by the charcoal canister.
Any real-world experiences and opinions would be greatly appreciated. The shop is very well-schooled and experienced with 951's, both stock and finessed.
Thanx,
Mark
Upon cold start or restart (within 30-60 minutes) the car will hunt for an idle. When the idle stabilizes a bit and I put a load on the car by driving away the car will stumble, hesitate and occasionaly burp out some black smoke.
The car had/has new Magnecor 8.5mm wires when the issue developed.
My shop has gone through the known suspects:
Smoke test for vacuum leaks shows only a small/"normal" leakage @ Idle Cont. Valve
Replaced Engine Coolant Temp Sensor
Turbo Bypass Valve checks as normal
New O2 Sensor
Replaced Throttle Position Sensor
Plugs replaced
Cap and Rotor replaced
Coil replaced
Scope pattern on Air Flow Meter (MAF) checks as normal
(Primary) Fuel Pressure Regulator replaced
Swapped out Milledge chips for OEM and vice-versa
Monitored the (Motronic?) data stream
Still no joy. Rough/fluctuating idle begins a few seconds after start-up , hesitation and stumbling under initial load still evident. Shop says that they theorize that the root cause of the issue is probably being masked when warmed up as the O2 sensor does its' job.
Next steps for the shop is/are to attempt to isolate the operation of the Idle Control/Stabilizer Valve and the operation or contribution to the symptoms by the charcoal canister.
Any real-world experiences and opinions would be greatly appreciated. The shop is very well-schooled and experienced with 951's, both stock and finessed.
Thanx,
Mark
