Engine problem

[Tobs]

My chim (400 1995) has just developed a problem that only occurs when it's hot (after a drive of 15 mins or so). Idle is very erratic - goes up to about 2000rpm and then back down again to 500rpm - miss firing and eventually stalling. It runs OK when you give it some throttle though. I have cleaned the stepper, without success, and also tried disconnected it with the engine running - this doesn't stop the idle hunting, so I don't believe it is the problem. I am suspecting the ignition side of things as I noticed the nearside precat glowing last night when I had the bonnet open and was checking the ignition wires etc.

Coil, dizzy cap, rotor arm and leads are about 2 moths old. Plugs are about 2 weeks old. I have still got my old leads dizzy cap and rotor arm so I may try replacing them. I may also try a new ignition module - or perhaps try cooling the one on there when I have the problem and seeing if this solves it.

Anything else it could be?

[poorpeet]

Lambda sensor? Follow the wire from the sensor on the exhaust to a push fit connector. Take it apart & make sure the contacts are clean. Do this for both sides. If this does not work take it to a garage or injection specialist. The can test the sensors in place while you wait.

[Cider Andy]

The coolant temperature sensor can cause this kind of problem, but it's unlikely to cause the manifold to overheat. I think you're right: that'll be an ignition problem.

Check the plugs, they're one of the most likely candidates. They seem to soot up pretty easily and cause misfiring problems.

[Tobs]

Just been trying to diagnose the problem. Swapped dissy cap / rotor and coil for some old ones I had - same symptoms occurred - rough running and erratic idle / stalling when the engine was hot. Swapped the coolant temp sender for an old one I had - no difference. Also reset the ECU still the same!

Took out the plus to swap them with some others and noticed they were VERY sooty - this could account for the idle probs. New plus in made no difference - were OK to start but sooted up again!

Problem now seems to be getting worse.....

Checked voltage from airflow meter - indicates about 3v! at idle, and 1.5-2v! just with the ignition on. This seems very high compared to the values in the bible so I think I’ve found the problem.

I noticed that when I disconnect the flow meter the engine will actually idle at a constant rpm, although slightly roughly. Is this the 'get you home' mode of the ecu?

I now need to find another airflow meter to try... I might look on e-bay...


Toby

[rfisher]

www.pistonheads.com/sales/64328.htm

May be helpful.