91' 240sx---idle up and down after warms up

[510SX]

My idling problem occured right after I crossed a nasty railway track at high speed. My butt still hurt.

What my car now doing is; after it warms up, the rpm rises slowly by itself to like 1500RPM and then quick drop to about 1000..

I also noticed the car is now running real rich, and miss fire intermitently at high RPM. (I changed the plugs and wires)

I checked the ETS, MAF and TPS (voltage, ohm and ground check on these sensor). They are ok except when I disconnect the TPS connector while the car is running, the engine stall. If I recall correctly, it didn't do it before. The fuel pressure is at 36 PSI at idle. I replaced the fuel pressure regulator but didn't help. I hope my pressure gauge is no good.

I am running out of idea; don't know what to check next. I am not sure I have mulitpule problems or just a problem causing ripple effect.

Any suggestion?

Thanks in Advance

[s13sr20chris]

will it start back up after you have the tps unplugged? it should start back up and run at base idle. if not the base idle is too low. also check for vac leaks. this is done by spraying everywhere with carb cleaner to see if the rpms rise.

[510SX]

will it start back up after you have the tps unplugged? it should start back up and run at base idle. if not the base idle is too low. also check for vac leaks. this is done by spraying everywhere with carb cleaner to see if the rpms rise.

I haven't tried to start it without the tps plugged in, but I tried to spray everywhere, no sign of vac leak.

[510SX]

S13sr20chris,

I've just started my car without the TPS connected per your suggestion. The car starts, but it runs real rough; like running on three cylinda. While the car was running, I saw some grey smoke coming out from the EGR/IAA area slowly. I haven't been able to locate the smoke yet. It smells like rich exhaust gas (it's not raw gas smell).Help me narrow down where the source of the smoke from. EGR, EPT, IAA...?

Thanks in advance

[s13sr20chris]

your sure it is not just carb cleaner burning off? is it just idling low? egr could be leaking from one of the gaskets or tubes. there isnt really much else back there that could be smoking. i would imagine it is exhaust related.

[510SX]

It's not carb cleaner burning off. It smells like the exhaust smell of an old muscle car. Anyway, I don't think the smoke is related to my original idle up and down problem.

BTW, how can you tell if your car is in fail safe mode? Currently, my car won't rev over 2300rpm. The car just keep choking, if I hold the rpm to about 2000-2300. I can't really tell if my car is in fail safe mode or actually miss firing.

[s13sr20chris]

fail safe will have you stuck in third gear. is yours manual? if so then there is very little fail safe for you to have. if its like a revlimiter then it sounds like a maf problem. maf failsafe will give you a rev limiter around 2200 or so.

[510SX]

Yes, mine is manual.

I think I found the problem, please take a look at my other post (Air Flow Meter spec?) if you can confirm my problem

Thanks Chris