Engine kills

[Pat S]

'91Q---Wife reports engine miss, stumble or lack of power.

I cannot get it to act up while driving, however while checking for the obvious, CAS, MAF connectors with engine idling, no problems appear when wiggling these connectors. When I finish checking these connectors and while scratching my head, the idle speed drops and the engine kills. Restart and it goes through this cycle again....almost like some control is reducing the idle speed....like once the engine warms up for example.

Any ideas?

[elwesso]

Fuel pump... Have the fuel pressure checked to verify....

[Pat S]

Changed fuel pump about 3-4 Mos ago.

[elwesso]

Is the filter new as well???

[Pat S]

No.

[psychic_mechanic]

A mostly clogged filter would probably effect WOT more than idle, it only takes a couple of dribbles of gas to idle the car properly.

Did you check to see if there are any codes in the ECU? Sometimes they can help narrow down a wide search to a system.

Mine has been doing that erratically at idle sometimes, I'm going to try an IAC / TB cleaning to see if that helps. (It can't hurt)

-Vinny

[Pat S]

I bought a new fuel filter when I ordered the pump from Scottsdale. Had a hard time removing the lines (couldn't remove them) from the existing filter......sooo.....I have not yet changed it. Do you think that the filter could be slowing fuel flow...seems fine @WOT. Any suggestions on removing these lines w/o cutting them?

[Pat S]

Thought about running codes. Aren't they displayed on the HVAC display...mine is out (the display). A/C works great any way. Thought about temp sensor for ECU may be giving a false reading causing ECU to adjust idle so low that it kills, but I ma not so sure that that is how it works.

Guess it is time to pull out the FSM and do some reading.

Thinking about bringing the cat to the dealer for a Consult....maybe check out some G35 loaner.

[TorQue45]

Quote »Any suggestions on removing these lines w/o cutting them?[/quote]

When I replaced my fuel filter, I relaced the lines as well. It makes the job quicker and easier. The lines can be purchased for about $3 at any autopart.

[Pat S]

But the stock lines look so good w/their perforated protective sheaths.

[elwesso]

No the ECU codes dont read out through the HVAC.

WHen the fuel pump was changed, was it changed as preventative maintenance or because it failed? You might be looking at a fried FPCU.

[Pat S]

Was changed due to humming....unit did not fail...preventative maintenance.

Just got back from rescueing the wife Q killed @ 4way stop (it will kill @ idle) I drove it home keeping the revs up @ lights, stops, etc.

Still goes like hell @ WOT!

Dealer Consult looks tempting! Wonder how much they charge for diagnosis only!

[DAEDALUS]

But the stock lines look so good w/their perforated protective sheaths.

The sheaths slide off. See if they'll fit generic 5/16" fuel injection hose. If not, you can shell out a bit more and get a roll of hose from Scottsdale.Consult will probably cost 1 hour of labor. Labor rate is constant; it's best to negotiate on labor time. 1 hour is min I think. You can get a fuel pressure gauge for about $35. Not as good as a Consult of course, but if you want to DIY, it is absolutely essential every now and then.

[Pat S]

That's right, I took a look at the fuel lines and the sheaths are separate. I am doubtful that the fuel filter is the source of my problem, however.

I think I'll call the dealer tomorrow. I hate dealing with dealerships and their service departments. When I had the dealer change my guides and chains (Inegotiated the price and I supplied the parts) the tech did such a sloppy job (Clamps not replaced on hoses, broken electrical connectors, RTV fingerprints over everything, etc.) I insisted that they correct all of these shoddy conditions. Took the dealership about 3 weeks after the initial work to repair/replace all of the above damaged components. I had their loaner for a total of 4 weeks, an I30...not a bad car, but not quite the match for my 10+yeay old Q.

[Qdemption]

It wouldn't hurt to use some di-electric grease on the MAF and CAS sensors. you never know..

How much gas is in the tank when this happens?

[Q45tech]

Unplug the electric connector to IAC the idle should drop about 50-75 rpms to say 500-550-600 rpm IF everything is clean and the IAC is only supplying 10-15% of the required air. With the other 90-85% leaking under the closed TB and thru the IAC bypass screw chamber.

Sounds like dirty TB/IAC to me.

OF course you never known seen lots of shade tree misadjustments of TB screws lately.

[Pat S]

Stopped by mechanic friend today. Hoohed up Snap-On Scanner/code reader and pulled an 11 and 12 code. MAF appears to be functioning correctly @ time of reading...I had a problem w/MAF connector a few days ago...cleaned and lubed w/di-electric grease. Thinking about ECU temp sensor as culprit. We cleared the codes and I have had no further sympyoms...yet.Will try cleaning TB/IAC next.

[Pat S]

Ok, I've been driving the car the last two days to experience the symptoms reported to me by my wife (primary driver).

1. Starts and idles fine.

2. Miss and stumble after driving 30min or so but only @ low/part throttle/light load...1500-2500rpm (like once you reach target speed and maintain).

3. Last episode resulted in engine eventually killing even w/my best efforts to nurse the throttle to keep it running...it just bogged down (like too rich) and killed. Pulled over tried to restart and eventually restarted w/WOT cranking. Immediately put into gear w/foot on brake and one on gas, accelerated and held it in 1st gear @ WOT....car cleared it's throat and accelerated strong (normal) and ran fine after that.

4. Next time driving, caught miss/stumble early, downshifted @WOT and problem went away.

5. Unpluged IAC while idling....no change in idle speed. Removed IAC (is this same thing as AAC valve in FSM?) Cleaned (wasn't dirty) and checked that valve & rod moved freely. Cleaned TB and re-assembled all. Will test drive next.

6. How do I verify correct function of IAC? And would IAC come into play @ part throttle (this is when problem occurs) or only @ idle? Also, have never made any adjustment to IAC or TB.

[Q45tech]

The IAC increases duration [solenoid open time from 10% at idle, 20% in drive but stopped, 35% AC on, to maybe even 80% at speed] to track the speed so that when you suddenly let off throttle the engine doesn't choke for air with a closed throttle.........the IAC progressively drops duration [in steps] as the speed falls.

Did you set the IAC bypass screw 2.5-3.0 turns out from the full closed [bottom position] ....."Unpluged IAC while idling....no change in idle speed.""""""" ?????? something set wrong.

Without KNOWING that the fuel presure/volume is ok [always while the stall occurs] or no codes in ecu, you must continue checking everything.Try and find a used [but working FPCU] and swap.

[Pat S]

Checked connections @ temp sensors. ECU temp sensor connector caused increase in idle speed when wiggled. Removed connector (boy are these connectors brittle...just look at it and it cracks) found corrosion...cleaned and replaced.

Going for test drive.

[Pat S]

Still Kills.

If I place car in drive with a/c on and disconnect IAC, should I notice a change. I had no change in idle w/car in drive when IAC was disconnected.

Thinking about driving to T-3.

[QShip]

Thinking about driving to T-3.

That's the best thing to do.