1990 240DL Sedan

I am trying to get as much info before seeing my mechanic tomorrow morning. Two symptons:
- 2-3-2 code indicated a bad idle.
- a noise that sounds like a possible exhaust leak (my description is like a card in a bicycle tire)

They may/may not be related.

Causes might be:
- rear exhause manifold gasket where I know there is a small leak, BUT it has been there for at least a year
- oxygen sensor never been replaced in 140,000 mile (or since day one)
- or ?

Feedback on this forum suggested replacing the oxygen sensor first. But could it also be a bad head gasket? AND if so, what are the typical symptoms?

A search of this forum indicates the symptomes for a bad head gasket are:

- water in the oil pan - I don't know
- smoke from the engine - No, not my problem
- smoke from the tailpipe - No, not my problem
- engine heat up excessively - No, not my problem
- loosing coolant that is evaporating inside the engine - I do not believe so
- (From another forum) a "fffhht-fffht" noise that indicates an open channel between two cylinders - Well this *could be* the sound I am hearing
- other?

Any feedback on the possiblity of this being a bad head gasket problem?

 

With a cold engine, start the car, wait 30 seconds and loosen the coolant cap, if theres any pressure the head gasket is blown, the combustion pressure is greater than the coolant pressure, especially seeing as the engine coolant is still cold so the cylinders build pressure in the coolant bottle.

pfft pfft could be a loose O2 sensor too, or the donut seal at the flange joint just in front of the cat, had that go on me last yr.

My O2 sensor is 200,000 miles and original. but you never know.
Check your fuel pressure regulator , pull vac line ,look for gas.
if its leaking that will trigger the 232 too rich.
It leaks down the vac line straight into the throttle body...too rich.
O2 sensor will trigger 232 too lean.

an exhaust leak might thrown the O2 sensor off if its upstream of the sensor.
Fixing the leak and clearing the codes might do the trick.

 

A bad headgasket? It'll stay out late, drink too much, be abusive, damage property etc.

But seriously, you don't have a bad headgasket. I bet it's all exhaust leak.
The thing with exhaust leaks is that they only ever get bigger, and they do it slowly. So that sound you have been ignoring has probably been getting louder over time as the hole opens up. In fact, at this mileage, just go over the whole exhaust and check for any telltale black streaks where gases are leaking. It's great to out the car up on stands, start the engine and run a hose held up to your ear around all the exhaust joints. I bet you find a few leaks.
Replace the gaskets and your problems will probably go away. I'd also replace teh o2 sensor, they have alife expectancy, and they're cheap enough, plus the side benefits are worth it.


Regards, Andrew.