Worked on 300E, now it stalls with idle valve connected! - PeachParts Mercedes-Benz Forum

pawoSD · #1 12-04-2008, 12:52 AM

I did a bunch of work on our new 300E over the past couple days attempting to solve a cold-start problem.

Symptoms: Car is very hard to start when cold, but starts ok when warm, once started and let run a minute or two, it will never stall out. Idle is very low (500) at all times.

Those were the original issues.

I replaced the idle control hoses (NOT FUN), cleaned the idle control valve, checked all sensor connections, installed a brand new OVP relay (old one had blown fuse but they wrapped wire around the base!

)

I get it all back together, begin cranking....nothing, nothing....battery weakening....so I hit the gas during cranking, it fires Right up and holds like 2,000 rpm with the pedal, I hold it around 1200 or so for about a minute, let off the pedal, it dies. The engine coasts to a stop, then the fuel pump shuts off about 2 seconds later.

I restart, it will fire, rev, die. I start using pedal, starts right up, I can hold the idle as low as 700 using pedal....let off, dies. I'm ready to set it on fire and get a diesel....ok maybe not yet. In desperation I unplug the idle control valve, turn key, fires right up! Idles at 750ish, smoother and more steady than ever before. In drive it lowers to 600. Check engine light comes on. I take it for a drive. It runs great, idles smooth, acceleration is strong.....0 issues. Come back, turn off for 10-15 mins......start it back up, fires right up and idles around 700.....I put it away for now, and we'll see tomorrow evening if it will cold start properly....(doubt it).

What did I do??

The engine wiring harness is Ultra-brittle....but everything seems to be plugged in ok (aside from idle valve). Why would unplugging the idle valve stop it from stalling?

Could my starting/idle issue be a weak coil? I don't want to throw parts at the problem.....that'd only dig the hole deeper.