M103 3.0-swapped 190E Runaway Idle Issues
07-07-2020, 10:44 PM
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1991 Mercedes 300E
M103 3.0-swapped 190E Runaway Idle Issues
I've been helping my friend with his project 190E. It was a 2.6 car but he swapped a 3.0 M103 with less miles in recently. After some issues with the torque converter that we solved, we got the car to start a couple weeks ago. However, after the car starts, the idle slowly rises from 2000 RPM to 3000 RPM, and once it gets there it more quickly rises to 3500-4000.
The throttle cable has a lot of slack in it, so that's not the issue, and the engine had all new gaskets/seals before it was put in. The main coolant temperature sensor (the 4 pin sensor on the back of the engine) is new as well. We believe the idle air control valve and the air potentiometer are working, and we don't believe there are any vacuum leaks.
With the air box off, if we spray starting fluid into the intake the RPMs will lower, and after a few seconds of spraying fluid it will die.
On a completely cold engine, it will start at 2000 and then increase to 3000 and then 3500 RPM or so after a couple minutes. On a warm engine, it jumps to 3500 almost immediately.
Has anyone experienced a similar issue, or know what may be causing this? We've thoroughly looked over everything and can't find anything that would seem to cause the issue.
The throttle cable has a lot of slack in it, so that's not the issue, and the engine had all new gaskets/seals before it was put in. The main coolant temperature sensor (the 4 pin sensor on the back of the engine) is new as well. We believe the idle air control valve and the air potentiometer are working, and we don't believe there are any vacuum leaks.
With the air box off, if we spray starting fluid into the intake the RPMs will lower, and after a few seconds of spraying fluid it will die.
On a completely cold engine, it will start at 2000 and then increase to 3000 and then 3500 RPM or so after a couple minutes. On a warm engine, it jumps to 3500 almost immediately.
Has anyone experienced a similar issue, or know what may be causing this? We've thoroughly looked over everything and can't find anything that would seem to cause the issue.
08-21-2020, 08:29 PM
#2
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Since you haven't gotten a response I'll take a stab at it. I can't speak for this platform itself but I had a similar issue with a '91 VW GTI, DIGI II car several years ago.
This particular car had a shorted trace in the ECU from bad engine grounds, resulting in the injectors running wide open.
I'd guess a fuel issue. See if your oil smells like fuel too. The car above eventually wouldn't turn over (hydrolocked) from so much fuel in the cylinders until I fixed the grounds, replaced the ECU pulled the plugs and evacuated the gas. I doubt your problem is this extreme but I'd suspect too much fuel delivery is a good start.
This particular car had a shorted trace in the ECU from bad engine grounds, resulting in the injectors running wide open.
I'd guess a fuel issue. See if your oil smells like fuel too. The car above eventually wouldn't turn over (hydrolocked) from so much fuel in the cylinders until I fixed the grounds, replaced the ECU pulled the plugs and evacuated the gas. I doubt your problem is this extreme but I'd suspect too much fuel delivery is a good start.
