What the hell is this??!!!

[Julio Bro!]

Please help: I have an idle problem since my '93 240SX SE overheated about 2 months ago, so the following are new - fan clutch, water pump, coolant temp sensor. Also cleaned the IACV unit and eliminated the PAIR valve (AIV). Heating was corrected, but idle problem with black smoke persisted, so last weekend I did the following - Changed oil, oil filter, fuel filter, new NGK V Power plugs and new oxygen sensor.

After the changes the car immediately felt OK, with no smoke; but after running a few miles that same day the problem began again with a twist. Now I have a rough idle with hunting...standing still for too long and the car stalls. Black smoke is constant, even at 2000rpm, and near 3000rpm the engine begins to jump...you know, the car feels jumping. Over 3000rpm things go better, but acceleration is not the same.

Today I'll change the cheap oxygen sensor I bought with the Bosch replacement, maybe that'll help. But I need urgent advice on what to do if this persists, I have my inspection check in November and I fear the worst.
Modified by Julio Bro! at 3:07 PM 10/19/2004

[Silvia007]

Overheated your engine... Yeah I think your head may be warpped.... sorry to say but you're lucky your car is still running.

[Julio Bro!]

Just changed the oxygen sensor, the cheap one was blown; a black, exhaust leak mark was on the under side of the unit. The new Bosch unit looks just like the original and coming back from where I installed it, the car behaved a lot better; no jumping or continuous black smoke.

It's back to the old patterned idle issue. Idles OK for say, 10 seconds, then goes up and down 3 times and repeats. It's like something is ending or getting empty or not getting enough. During the hunting, puffs of black smoke come out of the exhaust.

The car overheated, but not enough to blow the radiator or stall the engine...it just got the temp needle almost into the red.

[180fan]

check the MAFS and the wiring. my SR had an oscillating idle until it got warm, always pumped out black smoke and ran like crap until I figured it was the wiring. might be worth a shot

[DAEDALUS]

Hunting is very often a vacuum leak somewhere past the TB. Maybe the overheat warped the intake or the head.

[Julio Bro!]

I cleaned the MAF when the AIV was removed, seems fine. What is the TB?

I think a vacuum leak is a posibility, but to check on this the service manual talks about checking the "blow-by hose", what is it and where is it?
Modified by Julio Bro! at 8:19 PM 10/19/2004

[Tatanko]

TB = throttle body

[mss5413]

the blowby hose goes to your pcv valve. It is a lot of fun to look for so please read carefully. If you look down through the first or second crack of the intake manifold, you should see a hose connected to a threaded component. This is your hose and PCV valve. The easiest way to get to it is to remove your oil filter and the bracket right next to it. The bracket has two bolts on top and one on the bottom. Now you can take a pair of needle nose pliers and squeeze the clamps on the hose so they can slide back. Next use a socket and long extension to remove the PCV valve so you can check to make sure it rattles when to shake it, if it doesn't rattle, REPLACE IT!(3-4 bucks). The hose is about 9 inches long or something like that, I don't really know, and sorry I dont remember the socket size for the valve, but good luck anyway!

[Julio Bro!]

Hmmm, so the PCV valve may be a source for the idle problem?
Modified by Julio Bro! at 8:52 PM 10/19/2004

[toptechracing]

To start have you checked the ECU for codes?

Second since you over heated it are you sure you didn't loose a head gasket.

Third if head gasket is ok then you description sounds a lot like a coolant temp sensor.

[navysnail]

my car was doing somthng similar for a little bit, the maf connection was a little loose and when i was checking things, i accidentaly bumped it with my elbow and it instantly roared to life again, you might want to check that

check the hose that goes to the idle control valve, make sure it doesnt have a hole in it

here is a trick for finding vac leaks: take some carb cleaner and spray it around on stuff, if you spray it on somthing and the engine speed drops off real quick, you found it

[Julio Bro!]

I haven't check the ECU codes, I suppose that's my next step. Already changed the temp sensor.

That's a nice trick 240kid and I'll check into the MAF connection.

[Julio Bro!]

Well, before I could go with checking codes and the MAF, the cooling system broke the line that goes to the heater...back to the heating problem.

This is almost impossible to reach for me, so I had to take my ride to the shop. There, after repairing the broken hose and replacing the "out hose" (took most of the day for the mechanic to find a suitable hose), they tested for the MAF, with a good one from another car, and the idle problem went away.

So, now I need a new MAF, but OEM here is $700 (GAAAGHH!!). I'll be checking around the Forum, but what do you recommend for replacing a faulty MAF or is there a suitable performance unit?

[frapjap]

I sent you an email, I've got an maf from a dohc. 91-93 series.

[Julio Bro!]

Check your e-mail frapjap, I've sent 2 messages already.

[Julio Bro!]

Check your e-mail again Frapjap.

['97LE]

hey Julio Bro!,

my 240 had the same problem... is your engine leaking any oil or anything? (mine did a little bit) once it started doing all that... i MAYBE got another 1000 miles out of the engine before it blew.... so i am going to have to agree with the guys and say that your head might be warped... and start saving some cash b/c you might have a blown engine pretty soon... i hope i am wrong!

[Julio Bro!]

Man I hope that's not it. I do have an oil leak, but it's been there for years. Anyway the shop's supervisor told me he got the codes, but didn't explain...tomorrow I'll check them out, if there is bad compression something will show.

I'll be getting an MAF soon and I do hope that closes my case.

['97LE]

i hope the best for ya man... but life tends to kick you while you are down. keep us filled in with what's going on and if it gets fixed. oh and trust me, fix any leaks you have right away (esp. oil leaks). i kept putting mine off and look where it got me... BLOWN ENGINE!

best of luck!

[Julio Bro!]

This is, apparently, the end of this story. I took back my car with the cooling system repaired and expecting the idle problem to still be there. To my surprise, the idle was very nice. I thought, well, once it gets warm it will fail; but nothing happened, it even accelerated better than the last 2 or 3 months and no smoke whatsoever.

Got a look at the printout of the Self-Diag Results that the mech. supervisor left in my seat. The MAF had 9 hits and the speed sensor got 41; today I asked that supervisor about this info and why the MAF wasn't failing now.

He said that the mechanic, after testing with the other MAF, before re-installing mine did some cleaning of the connections. Also, and problably most important, pressed together the pin connectors for a tighter fit.

Add to this that the codes were cleared and now I don't need a replacement MAF; unbelievable huh? The bill was $194, but they let me go with $174.

I don't know if the speed sensor has been bad, or what problems it may cause. But I'll check which plug is it and clean the connections good, then a press of the connecting pins should make things tighter and better, I hope.

Well, I'm happy for now, but I still want to buy another MAF just in case mine fails later and will be watching for that oil leak. I'll post these tips so that everyone can benefit from my experience.

Thanks for all your help.