126 300se warm-up question - PeachParts Mercedes-Benz Forum

fahrgewehr2 · #1 09-05-2003, 10:31 PM

Hi all,

Have a question. 90 300se - is MUCH faster off the line (much more power) when first starting out in the morning. After motor is becoming warm (temp gauge is between 50 and 80C) there is a hesitation. After car is fully warmed up, everything is smooth, but engine is not as fast as it is when it first started.

I hope this is not confusing. I have seen 2 posts with this same question in the past, and neither recieved a reply.

O2 sensor is new. Mileage at 20mpg. Car starts cery easily. Valve job done 20k ago. Getting 50% flucuation at warm idle.

Mystery...any ideas?

Mike

fahrgewehr2 · #2 09-08-2003, 10:55 PM

Anyone? Any suggestions would be nice. Thanks, Mike

BobK · #3 09-09-2003, 12:36 AM

Sounds like your warm up regulator is a bit goofy or perhaps you have a bunch of vacumm leaks and the rich mixture when cold is compensating for incorrect air-flow reading. Usually there is a procedure and table for testing the regulator with a presure gauge and valve. Remember making my own to work on CIS VWs a long time ago. JC Whitney had one for less than $60 and I may just buy one. That control presure is almost everything to the CIS system.

fahrgewehr2 · #4 09-09-2003, 01:26 AM

Thanks for the response Bob. I too suspect vacumm leaks. The vacumm hoses in the engine compartment are pretty cheap on fast lane (sold by the meter) so perhaps I should replace them all and see what happens. Shotgun diagnostics, I know, but cheap.

Where is the warm up regulator located?

Thanks again for your response. Mike

BobK · #5 09-09-2003, 07:58 AM

Figures I should look a the CD before talking. They don't use an old style warm up regulator for control presure on these engines. Looks like it is all managed with the EHA (on the side of the fuel distributor) and the diaphragm presure regulator. Just means that you have to check the sensors. Big one here is probably coolant temp sensor. Looks like it should be 2.5k ohms cold and 340 ohms hot (all readings plus or minus 15%).
Replacing vacumm lines can't hurt. As the engine ages, little vacumm leaks always creep in. You get enough of them and it gets beyond the ability of the lambda system to make up for them. Keep an eye out for gaskets going bad. You can usually spray a little carb cleaner along the gaskets and listen for an RPM change to spot where the gasket is bad. Sealing rings at the injectors are another place for leaks. Some folks just replace them to be sure.