Discussion
I wish was too much cam but I'm sure it is FI related. (US 280i)
Sometimes - and it can go days without this problem - at foot-off the gas idle (or more precisely was I come to a stop with no throttle and wait) the engine goes into a loop where the revs drop, the tac drops to 0 RPM, the red light comes on, the revs pick up, the tac jumps up to say 1500 and the cycle repeats. About a 1-2 second cycle. Giving it gas smooths out the problem but if I let off the gas, the cycle usually restarts. Normal idle is rock steady at about 1,000 RPM.
Seems like a bad feed-back loop. Any ideas where to start looking? Thanks Grady
Sometimes - and it can go days without this problem - at foot-off the gas idle (or more precisely was I come to a stop with no throttle and wait) the engine goes into a loop where the revs drop, the tac drops to 0 RPM, the red light comes on, the revs pick up, the tac jumps up to say 1500 and the cycle repeats. About a 1-2 second cycle. Giving it gas smooths out the problem but if I let off the gas, the cycle usually restarts. Normal idle is rock steady at about 1,000 RPM.
Seems like a bad feed-back loop. Any ideas where to start looking? Thanks Grady
The Ford FI is a tricky system, so I hear.
I would initially eliminate some simpler things. For example, the electrics. If the revs drop, the alternator kicks out less juice, which makes them drop more. This can lead to near stall. One thing to try is a fresh battery - or at least, put the battery on charge for 48hrs and then see if it happens again.
Other loads on the engine worth checking are PAS and air con, if you have it.
One gotcha that caused one of my friends loadsa hassle on a 280i was that the fuel return was restricted, which led to overfuelling and poor idle. (Yes I'll be checking this on my 350i too!!!)
I would initially eliminate some simpler things. For example, the electrics. If the revs drop, the alternator kicks out less juice, which makes them drop more. This can lead to near stall. One thing to try is a fresh battery - or at least, put the battery on charge for 48hrs and then see if it happens again.
Other loads on the engine worth checking are PAS and air con, if you have it.
One gotcha that caused one of my friends loadsa hassle on a 280i was that the fuel return was restricted, which led to overfuelling and poor idle. (Yes I'll be checking this on my 350i too!!!)
Grady,
I second the "charge the battery" just to eliminate it.
Assume you listened to fuel pump.
Did you pull the wire off the frequency valve?
Then pull the O2 sensor wire?
One is before the ECU one is after.
After that...do you have a CIS type pressure guage
?
You'll have to look to see whats happening to the control pressure See if it drops and the system press stays high or if they both drop together.
You could give your sensor plate a push just to make sure it isn't sticking, although I doubt that would give the cycling rpm it would just stall.
I second the "charge the battery" just to eliminate it.
Assume you listened to fuel pump.
Did you pull the wire off the frequency valve?
Then pull the O2 sensor wire?
One is before the ECU one is after.
After that...do you have a CIS type pressure guage
?You'll have to look to see whats happening to the control pressure See if it drops and the system press stays high or if they both drop together.
You could give your sensor plate a push just to make sure it isn't sticking, although I doubt that would give the cycling rpm it would just stall.
jeff m said:
Grady,
After that...do you have a CIS type pressure guage?
Thanks Jeff - Don't have pressure gauge but it appears to be as simple as corrosion in the one or both of the thermo sensors plugs. Disconnecting either caused the the symptoms to appear. After that...do you have a CIS type pressure guage
?I cleaned the plugs with circuit board cleaner and a dental pick, let dry and applied some di-electric grease. I plugged them back in and the idle smoothed right out. Hopefully it will stay fixed as the weather was bad and I couldn't take a test run. Grady
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