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Hello all,
Apologies in advance for a long post, but I want to be thorough.
My 1993 944T (145,000mi) has the following symptoms:
1. On the first start of the day, when the engine is cold from sitting all night, the idle will surge between ~200 and ~1500rpm at the first stop light I get to, usually within 3-5 minutes of starting the car. After the engine has warmed up a little the idle stabilizes at about 750rpm when the car is in gear, and the problem doesn't come back until the next stone-cold start the next day.
2. When the car is in gear, the idle is a steady 750rpm. But when the transmission is in Neutral or Park, idle jumps up to ~1600rpm.
3. When I let off the throttle and coast, idle drops to about 1000rpm before swinging back up to the normal coasting speed of 1500rpm.
4. When the engine has warmed up after 20-30 minutes of city driving (ambient temp has been about 40 deg. F here), the engine speed will drop precipitously under moderate to hard braking from 35-40mph+. Sometimes it will recover but usually it just dies, but will re-start immediately. Blipping the throttle to keep the idle up prevents a full stall, but that's not what you want to do when you're braking!
Here are the steps I've taken to remedy the problem:
1. I tested the AMM using a multimeter according to the procedure in the FAQ, and all readings came back within range.
2. I tested for vacuum leaks around the intake manifold by spraying the gasket areas and injectors with WD40 with the engine running, but found no leaks.
3. I tested the check valve on the line from the brake booster to the intake and found it to be working properly.
4. I removed the IAC and cleaned it with carb cleaner (I don't have the kind you can disassemble so that's all I could do), which seemed to help a little bit with the cold idle issue, but not much else.
5. On Spook's suggestion I tested the crank position sensor harness by wiggling it with the engine running to see if there's a bad electrical connection in there, but everything seems fine.
6. I replaced the Fuel Pump Relay and Radio Suppression Relays with brand-new units, to no avail.
The car's air filter is about 5000mi old. There is an exhaust manifold gasket leak on the #1 exhaust runner, but I don't see how that could be contributing to this problem.
So, do I need to spend $150 on a new IAC, or is there anything I've overlooked? Thanks for reading the lengthy post!
Jeff
1993 944T
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