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Hi Dave:
Lately, my 1984 Ford Escort GT (EFI, NOT turbo, still in impeccable condition @ 84,000 miles) suddenly surges to 2000rpm when idling, just after starting. What happens is that when I start from cold (at this time of year, ambient is 54F), the engine races to 2000rpm straight away. So I hit the gas, and idle speed comes down to a more normal 1100rpm. Then, after about 30 secs (car still stationary), it jumps to 2000 again. If I am driving by this time, this results in a brief hesitation/jolt. The problem disappears when the engine warms up. My average gas mileage has not changed ever since this problem arose.
I would really appreciate your help in this annoying problem. Thanks.
Robert
Answer -
My service manuals only go back to 1995 for this vehicle, but I will try to offer some advice. Idle surging or "rolling" is usually caused by a vacuum leak, but this normally happens at all temperatures. A common cause for a "high" idle is a bad Idle Air Control (IAC), this could stick a different temperatures. Another porblem could be a Manifold Air Temperature (MAT) sensor, this could be giving the computer incorrect infomation. I would highly recommend having the vehicle diagnosed before replacing any parts. I am not sure that this engine has these sensors, and I wouldn't want you to waste money on non-returnable parts.
Sorry, I couldn't help more,
Dave
Thanks. I don't think it's a vacuum leak or sticking ISC, as the problem would occur at all temperatures. It seems to be a cold engine (i.e. "choke") problem, probably electrical/electronic in nature. I know how to acquire fault codes from the ECU using an analogue multimeter, so I will try that (I have the '84 Ford Factory Manuals). If the problem is a sensor, as you suggest, this will hopefully show up as a stored fault.
Robert
AnswerIt would be a good idea to first check the system for trouble codes. When a code is set, the system turns on the Emissions light to warn the driver of a problem. Sometimes a sensor can be working improperly or stick within its normal operating range, the computer would not see this as a problem, and would not turn on the Emissions light. If this engine is EFI, it would not have a "choke". The computer senses the engine's conditions and increases the fuel mixture.
I hope this helps,
Dave
