New 240 bad starting and rough idle.

[James k]

Hi,

This is my first post here. I've just purchased a 1991 240GL which I picked up yesterday. It seems to drive fine and handled the 100 mile drive home yesterday with no problems but it has a rough idle and starts very rough. When you start the engine, the engine is really rough and needs revving for about ten seconds before it settles down. It's then okay but slightly lumpy. The fault light was on so I read the codes and got 212 and 113, signal missing/faulty from oxygen sensor and fuel trim too lean.

I thought I'd ask on here before just changing the O2 sensor in case there's anything else I should be checking.

Thanks,
James

[Moomoo]

I can’t help with your problem, others will but welcome along!👍

[Blitzp]

Check fuses at the left in the passenger footwell. my o2 sensor wasn't getting a signal and it was a fuse that looked alright until i removed it and it sprung open.

the fuel pump relay will be behind the trim below the glovebox. its a fairly big white block. tray taking it out and giving it a gentle tap and putting it back in to see if that helps with the lumpiness. if it does it may be needing replaced or one of the fuel pumps might be causing it to stick on if they aren't working properly.

ive just changed my in tank and external pumps as one was causing the relay to stick.

[James k]

I checked the fuses and all seems good there, correct voltage.

I did some servicing today to get the baseline sorted. New plugs, leads, distributor cap, rotor arm, air filter and oil change and filter, cleaned the MAF. Still idles rough!

I investigated the O2 sensor problem a bit more. The sensor output voltage isn't fluctuating between 0.1 and 0.7V, it's just steady at 0.6V. Reference voltage is correct, supply voltage and found are both good on the O2 sensor, Ground is fine on the MAF. I couldn't check the voltages on the MAF as I couldn't work out how to probe the connector with the MAF plugged in. Assuming those are correct, though, it looks like the O2 sensor is indeed faulty!

I sprayed brake cleaner around the inlet manifold, injectors, vacuum hoses. Nothing happened so it looks like there aren't any air leaks. There was a hint of smoke from the oil filler cap when I did the oil change, though, so I wonder if the crankcase breathing is in order.

I'm going to order a new O2 sensor and see if that fixes it. Does that all sound correct?

Thanks,
James

[Blitzp]

normaly if you put something over the oil cap it should try to suck it in if the crank case ventilation is blocked it would try to push it away (i think).

have you changed th eO2 sensor? did it make a difference?

have you looked at the timing?

[James k]

I've now replaced the O2 sensor and the code hasn't come back. Running is a lot better. Idle still isn't completely smooth and it needs revving a bit when you start it still. It kicks a lot when it starts, makes the car jump.

In general, it seems to be running well, though. I'll do the check on the filler cap that you suggest.

[Blitzp]

just keep a hold of whatever you use just incase it decides to take a trip into the camshaft