1992 300SE Sluggish

[GTO71]

I have a 1992 300SE with a M104 that starts right up and is very responsive for about 2 minutes, then gets sluggish an accelerates like a snail and will rev very slowly. A quick cycle of the ignition will shortly bring the car back to normal for a minute or so them its back too the sluggish stuff again.

I just replaced the throttle valve (body) assembly with a junkyard unit and it is the exact same....any thoughts?

[oldsinner111]

I quit answering most,as there's always a smart arse that will tear down what you say.

[Diseasel300]

Out of curiosity, does this reluctance to rev occur in park or neutral? If so, have you checked for back pressure in the exhaust? Sounds suspiciously like a clogged catalytic converter or muffler. Typically if you're having running problems you'll be getting rough running, misfires, backfires, or detonation (pinging).

[GTO71]

No it will rev the same in gear or park/neutral. A quick cycle of ignition will quickly switch the car back too normal...this appears to be an electronic issue not a mechanicial one.

[Diseasel300]

Being a 1992 vehicle, I'd imagine you're still CIS? If so, throttle and fuel control are MECHANICAL. Putting your foot down is a mechanical action on the throttle plate and fuel delivery is a function of air moving across the metering plate.

If the engine will rev in neutral or park when first started, but won't after running for a couple minutes, you have a problem somewhere that's restricting performance. Shutting the engine down and restarting will allow a clogged exhaust to bleed off pressure quite rapidly. Once you restart, you're fine until pressure builds again.

If you had an electronic issue it would be spark or mixture. If you have spark issues, you'll smell raw gas on the exhaust. If you have a mixture problem, you'll be smelling gas if rich, or hearing detonation (pinging) if you're lean.

[Ferdman]

GT071, when was the last time you replaced the fuel filter and the Oxygen sensor?

[GTO71]

Originally Posted by Ferdman

GT071, when was the last time you replaced the fuel filter and the Oxygen sensor?

Well, I just got the car a week ago..for $700. The interior is mint and the body is very nice. The vehicle was maintained at the dealer its whole life but developed this issue and ended up with me. Maintenance was very good.

I am out of town and will check the main wiring harness when I get back.

[Ferdman]

GT071, any vehicle routinely maintained by a MB dealer's Service Department would not have the issues you describe. When was your 1992 300SE at a MB dealer last? It's likely the previous owner received a large estimate for pending repairs, and chose to sell the vehicle instead.

[sixto]

Is there a way to check for diagnostic codes like with a blinker box?

Sixto
98 E320s sedan and wagon