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1980 633csi with L-Jet system. Motor rebuilt about 5K ago. Ever since I got it back, the car will lose all power when at wide open throttle. It doesn't matter what gear I am in. Once I back off the throttle, normal operations continue. I cannot replicate this parked in the garage manually operating the throttle - car red lines before the high idle switch is engaged. I assume because it has no load on it.

I checked both throttle position switches for resistance, and both seem to be working. I adjusted the TPS plate per the Tech FAQ with no improvement.

The wires to the switch are both the same color (white), so I am hesitant to throw my meter on them to see if they are getting a signal from the ECU (don't want to fry it).

Car has some cold idle issues which I don't think are related as I had this throttle issue when it was idling fine.

Cheers,

Dale

I actually had nearly this exact problem on an 80 633 I used to have. Over half throttle and it would die. Turned out that one of the wires to the FI temp sensor plug was broken and would lose contact as the engine torqued and things changed position just a bit. But the odds of it happening again seem unlikely.

Check that, but try this. Disconnect one wire each from both idle and WOT switches and try it. The wires may have gotten moved at some point. Put tape on them if you want but they should stay in place. It doesn't need either to idle or run to full power. Well, you might be missing a little enrichment at WOT, but at worst it's fine for troubleshooting.

I agree with Mike.

As I recall, the ECU will cut fuel when the idle switch is depressed and the engine RPM is above 1200-1500 RPM. This is done to save fuel when engine braking. If you floor it and send the ECU an idle signal instead of a WOT signal it would, in theory, cut fuel and cause the engine to lean out and stop accelerating.

When the neither the idle or WOT switches are depressed, the ECU takes it's primary load signal from the AFM. You should be able to pull the wires off the idle and WOT switches and try again, if it works, there's your problem.

p.s. The idle and WOT switches are only low current signal switches, which typically run at 12 or 5 volt DC. Testing these is unlikely to damage your meter, but may damage the ECU if the pins are allowed to short to ground (i.e., any metal part of the chassis or engine).

Good luck!

Thanks for the feedback - still chasing this down, so this is helpful.

Dale

I spent some time on the phone with Ron last week, and finally got back under the hood. Besides the WOT issue, car was beginning to stall out intermittently while searching for idle.

I unplugged both throttle switches, and I have power at WOT and the idle improved. I am going to check again to make sure the wires weren't switched, but don't think so because the ones for the idle switch are short and won't reach the high throttle switch.

Still a little puzzled as I tested the resistance at the switches, and the appeared to be working on my meter.

Thanks for the help.

Dale

I have put about 100 miles on the car since disconnecting the TPS. Acceleration at the top end isn't crazy like I remember, but there is power. Interesting thing is my gas mileage is about 50% better, which leadss me to believe that somehow the ECU was telling the car to run very rich. Not sure if that would be due to faulty TPS, or an ECU issue

I'm guessing the MPG was because the ECU thought it was in WOT operation most of the time.

Hey Dirk,

I got thinking about the switches, you may have one lead from each switch mixed up, not both leads to each switch. You might want to see about tracking them back to the connector to see which one is which and verify they are both on the correct switch.

Ron wins the chicken dinner. I went back into car - harness was caught up and the leads to the TPS were caught up. Once I got them loose, I switched them. Appears to be working.

Cheers
Dale

It just made sense that the switches or what they were connected to was the problem from the way you described it. Now about the chicken dinner...