Mercedes-Benz Forum banner

1 - 1 of 1 Posts

1 Posts
Discussion Starter #1
Hi there, joined this forum to get some insight.

Here's my problem, car starts just fine and idles normally at 900 RPM, perfectly smooth. However as soon as you press the gas pedal, even if you barely touch it, the RPMs shoot up to between 2000-2500 rpm (still running perfectly smooth) and will only go back down if you put the car in gear. Once in gear everything is perfectly fine, Idles at around 900 RPM, doesn't seem to pull anymore than normal. But if you put it in Park or Neutral, the RPMs shoot right back up... Turn the car off and back on again, idle is perfectly fine in Park until you hit the gas and you're back to where you started.

Some background: I just finished replacing the head gasket. The car ran and drove perfectly fine before but it had been leaking oil from the head gasket for a while and it was getting to the point where it needed to be addressed. I was careful to make sure all of the vacuum lines went back where they belonged and even replaced a few cracked ones. The car does have 184,000 miles but has been well maintained.

At first I thought it was a vacuum leak but after double and triple checking, spraying carb cleaner around with no change, I'm pretty sure that's not the case. If it was a vacuum leak, I would expect it to have a high idle all the time and not just when I hit the gas as well as having a rough idle. The only check engine code coming up is P0507 High Idle

I tried the throttle reset stuff with no success. I did start the car with the throttle position sensor unplugged and with the throttle cable from the pedal removed. While it was running I plugged in the throttle position sensor and immediately the RPMs went up and didn't come back down.

I'm going to run out to the import junkyard tomorrow and grab another throttle position sensor to try that. I just wanted to also make a post to see if anyone had any better ideas or maybe can suggest a few more parts I should try picking up at the junkyard while I'm there.

One more thing that I think is irrelevant but maybe not; I also replaced the transmission electrical connection (was really leaking) and had to top up the transmission fluid. At operating temperature the level is correct.

Thanks in advance for the help!
1 - 1 of 1 Posts