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Friend has just bought an Escort to run to work. Has 16v 1.6 Zetec 90PS engine. The tickover from cold see-saws rythemically between 1600 & 500 rpm without touching the throttle. If you touch the throttle revs rise to 2000 & if you very slowly release the throttle revs steady at 600rpm. If the throtle is bliped again the revs see-saw as before. It stabilises fine as soon as the engine gets warm. Has anyone come accross this before & know the probable cure ? Thanks in anticipation.
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An air leak is the first check; the rubber breather hose [and the PCV valve on the end of it] is the most common place.
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Yes, I have with an early nineties Escort 1600, no doubt very similar. It is probably the idle control valve. My car did this quite badly and tended to stall unless run for at least a second or two on the overrun before coming to a halt. It also went through a period when the idle speed would be very high unless one blipped the throttle, but that stopped. My excellent local indy mechanic cleaned out the whole inlet tract including that valve, which is on the front of the inlet manifold with wires going into it. The car behaves much better now, although being elderly it isn't quite perfect. Make sure all the joints in the inlet tract, from the air cleaner through to the manifold, are properly closed and not leaking too much air. Take a look at the air filter and if it is filthy on the underside, replace it.
Listen to Screwloose who is a pro.
Edited by Lud on 06/05/2008 at 16:26
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Thanks for both your help. The air cleaner is brand new. I checked for any air leaks but all the pipes seemed tight & no holes I could find. I removed the idle solenoid, easier said than done. Tried to energise it from variable voltages from 5 to 12 but nothing moves. It allowes air to pass normally with a spring that keeps a plunger off its seat. When energised the solenoid should close the plunger against slight spring pressure. The solenoid doesnt move under electrical energisation but is free to move mechanically. I measured its resistance as 5.5 ohms. Presumably this indicates that the solenoid has failed in some way.
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Just an update to the above and another thank you to Lud & Screwloose.
I replaced the idle solenoid & the engine tickes over at a steady 1400 rpm from cold & drops back to 800rpm after a couple of minutes.
As it's not my car I don't know if this is normal but it's 100% better than the previous see-sawing revs, so seems ok to me.
I was wrong about the solenoid action, the partial opening of the valve when de-energised becomes a full opening when energised & the coil value of a good solenoid is 10.5 ohms.
Hope this helps anyone else with a similar problem.
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