Rough Idle with oil pressure dropping

crocodilehunter

Registered User
Hey guys, long time no see. Been a while. Anyways, my 90 XR7 has started to have a rough idle when in drive, and the oil pressure drops sharply every so often, and when the gauge reads on the L, or the lowest point, the car idles real rough, then it kicks back up a bit. When i drive, everything is normal. In park and neutral, everything is normal... So i have no idea what could be causing this. I checked oil, and its fine, i checked coolant, and no oil or bubbles in there, PHEW! Let me know what you all think.
 
same problem here....

Hey There....don't feel alone on this one. My 93 just started doing the exact same thing. I was about to post the issue when I noticed your posting. So, anyone???? I also wanted to add that on hard acceleration, I notice a slight lack of performance and possibly a little ping. Retarded timing??? This problem also seems to occur after the engine is up to operating temp. I've also noticed that is idle and oil pressure seems to drop when the fan kicks on. I'll probably try to pull codes one night this week, but if anyone has any suggestions, please feel free to let me know.
Tim
 
Check all of the ground connections!!!

This sound like you are have an electrical problem with the ground system. The symptom that points to this is the connection to the cooling fan. If you get no mechanical noise when the gauge drops, it is probably a false reading.

The oil pressure gauge is an idiot light, it is hooked up to a switch and is wired to read a pressure. If the ground is bad the gauge won't see the full 12V power and will read low. Also the bad ground can cause the DIS system to freak out.

Aaron
 
a mechanical noise, such as ticking or the like??? No, none of that, but the engine sags like it's going to die (and sometimes does). When I bring the RPM's back up the oil pressure gauge returns to normal and the car seems to run ok, although a bit rough. I guess an electrical issue could cause this. I'm going to check all the connections I can find as well as all the grounds. Is the oil "pressure" sensor one that completes a ground? Is there a chance that it's bad and is the cause of the whole problem? Thanks Again!
Tim
 
Here's what I would do, but its sort of up to you.

Replace the oil sender just to be sure its working properly and giving you good readings (a joke, as its really just a switch) they're cheap and they do break.

Look at the condition of your engine mounts! Collapsed mounts are sometimes the cause of most of the mystery low idle problems.

Used to be, I had difficulty parking the car as the engine would stumble, and whenever I turned on the A/C it would just plain die. All of my load-idle problems have dissappeared after replacing my mounts.

You may not be able to tell by just looking, but if the limit arms are resting on the bottom of the openings, or if the original mounts have more than 100,000 on them, they're toast!
Another sign is the oil filter is stuffed up against the subframe and almost impossible to get a wrench around.
 
Fuel Pressure

Heres my opinoin on what to do first check your fuel pressure at the rail. When the fuel pump starts to wear down it will cause flustering of the engine due to lack of fuel. It will cause lack of power and it will not get any better by itself. Just my opinoin but a cheap and easy place to start. If you fuel is fine then worry about the 100 things that could cause the spark or airflow to go bad.
 
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