Stumbling Q45: Bad Cycling at 2000 RPM, decaying idle just warm

[eagent]

Hi Infiniti Masters,

I drive a 90 Q that I've owned for 2 years (163,000 miles). It's a great machine overall (man, did they get the fit and finish right, or what?).

Anyhow, my Q has a real problem when it's been driven just a few miles (I do mean a few: 2-3, sometimes less).

It stumbles and lurches/dies/lurches/dies at 2000 RPM. It appeared to be a fuel starvation issue (that makes sense, right) or a vacuum leak.

Vacuum checks out fine on visual analysis. In searching around, I saw some commanilities with my problem and the fuel delivery mechanisms. So I replaced the Fuel Floe Regulator, and then the Fuel Pump. No change at all in the reaction.

Also, the idle decays in speed as the engine warms... starting at ~1000 rpm when really cold, then when it warms, it goes to 450-550 rpm. If I sit at idle dor a while, it will eventually just quit.

The Engine Light comes on some of the time, though it's intermitttent. When it's on, the condition is there, and exacerbated. When off, it runs good (for a short while, only when cold).

Any ideas? I'm at a loss, and coming from the Air Force as a jet tech (many moons ago), I hate being a stupid parts changer... I really want to intelligently know what's going on.

I pulled the battery positive off for 30 minutes tonight, thinking maybe the computer crashed, but no dice. Same problem.

Also, when it's cold, I can get the RPM up to 5000+ (haven't driven that fast lately).

Thanks much. I've seen Q45tech around, and his ramblings have been extremely helpful.

Best,ME

[Chally]

G'day ME & welcome to Nico. Hope you enjoy the site.

Check the terminals on the Air Mass Meter & the Crank Angle Sensor first, & make sure they are very clean. If that makes no differnce, try & get to a consult to check out what's going on.

Maybe Q45 Tech will know without the consult, but check those terminals, as it is good maintenance antways.

[Q45tech]

The car was designed assumming it would come into dealer every 90 days [3,750 miles] for an oil change! At that time any problems would be evaluated [pointed out by customer]..........why they built the very extensive diagnostic system requiring the Consult.

Because we have them handy I check mine every month for hidden codes [knock sensors and others] that don't turn the MIL on..........Obviously if the MIL comes on you have a very serious problem that needs checking out because the early Q were very tolerant and didn't light the MIL easily.

The 1200 decaying to 650 warm up is normal the 450-550 idle tells me the throttle body and IAC valve and system are very dirty and need cleaning to return to 650 rpm.

Get the to an expert on Q ASAP

[eagent]

Thanks a ton, Gentlemen. So here's my course of action:

1) Clean the connectors on AFM and CAS (looks like using dielectric gel is also preferred as a final touch?)

2) I did have a Throttle body cleaning 14 months ago, but will take it apart and examine... hey, could be this nasty gas we're getting down here in SoCal.

3) Get the dealer to run the codes, and work it from there.

Anything else that comes to mind?

Thanks a ton gentlemen. This is amazing having this level of Brain Trust available on such short notice (it's just past 7AM here in Newport Beach, and I have two posts from Inifiniti Guru's that really clear the air on this. Amazing!)

I'll post the solution when it happens.

Best,ME

[Q45tech]

"2) I did have a Throttle body cleaning 14 months ago"

At 163,000 miles the blowby starts to gets high.............I clean my 90 [245k] every 6 months at least [6-8k]............when ever the idle begins to show any slight change or instability.

On old worn engines it doesn't take long for a little carbon/oily vapor to settle in the critical bottom of TB where the 2 vacuum ports [tiny holes] are located!

Of course I am a perfectionist and expect an as new idle even after 13 years of service............most are far from perfect and shake rattle and roll at idle [or die as yours did].

[Q451990]

You can also check ECU codes at the ECU by manipulating the screw on the side of the unit and counting the flashes. If you have the service manual, check there for details. I'd lean toward bad MAF or CAS connections (need cleaning and some dielectric grease) first, but the ECU code will tell you a lot since you're getting the Check Engine Light.

Do you have a CA emissions Q or did it come from another state? The CA ECU will give you a little more feedback via the check engine light than Federal Qs.

Welcome to the club!

Heath

[eagent]

Hi Gents,

Excellent results so far, but still some intermittent stalling and rough idle when warm (except, of course, when the engine light goes out. Then the idle returns to normal, and the sucker flies!).

OK, here's what I found: 1) True to form, the contacts were white with corrosion, with a touch of green on the edges (and NOT green with envy). Being in Newport Beach, CA, we have plenty of sea air to destroy ANY metal. Looks like my contacts included.

2) Cleaned the contacts (couldn't find dialectric gel yet, still looking. The local Schuck's neglected to carry it. I'll do a Radio Shack run, or similar.

3) Once cleaned, the thing ran awesome... until it warmed. Then it started stalling, and you have to dance on the throttle pretty fast to keep it alive. Engine light then comes on, and you either die at the next light, or it almost dies, then comes back to the previous low idle.

4) Opened the hood once I got it home (whew!) and jiggled the MAS connector... and it gurgled and rumbled. I assume I just need more cleaning and the aforementioned dielectric goop to keep it golden.

5) Also noticed (for a while): I can shift into 1st (automatic trans), and it won't go there (or second, for that matter), as though the transmission has P-R-N-AUTO, but none of the selected gears. Also: when the engine light comes on, shifting it into the lower gears (on the console... 1 or 2) the light will eventually kick off. I wonder what the heck that's all about (bad vacuum hose, bad Torque Converter, some computer glitch?).

6) If I didn't emphasize "thanks" enough, let me do it again. Yes, the dealer will get his mits on it, if for nothing else, the codes. But you guys really nailed the major hal-mal. I can't thank you enough.

7) These message boards need a "Donation Station" for really good results. Something to help motivate you (outside of your true passion for this, which is evident). Maybe that would quell the whole deal, make it too money-motivated... but think about this:

a) I have spent roughly $400 in fuel pump and FPR (the pump was whining a little anyhow, so it was probably a good thing... I've heard the computer for that thing is yet another $350 or so).

b) My next move was... who knows. A dealer diagnosis, or a fire sale. I am reluctant to do either, because I love the car, and I've seen dealers try to sell me muffler bearings before, and I absolutely HATE that!

c) I could have become really good at parts changing, and wound up another $400 in the whole, then threw in the towel, and watched South Park until I regained my sense of humor about the whole thing.

Your words of wisdom gave me a path and clarity. Great stuff.

Hey, I know the guys at http://www.freshalloy.com pretty well. You ever thought about generating content for folks like that? Just a thought.

Thanks again. The beer's on me next time.

Best,ME

[DAEDALUS]

Great to see progress, and good call on replacing the fuel pump. I just bought some dielectric grease today from Pep Boys. It was in the RTV isle. NICO is working on the donations thing, but only so the site owner can start mitigating some of the major expenses of owning this site. Otherwise, all members are here just to show their love. Good luck getting your car back to purring and happy.

[Chally]

Are you shifting it to 1st as the car is moving?If you are, the auto won't go to 1st until it is under a certain speed.

I have also noticed that if you are in 2nd, the transmission is reluctant to go back to 1st when you floor it, as it would do if in 3rd or 4th.

[eagent]

Alright, alright...

So I've cleaned the contacts (I'm considering cleaning all of the remaining contacts under the hood... any comments? Am I just asking for trouble here?). I've run the car through it's paces... and... (drumroll please...;-)

She rocks!

Yup, it looks like these puppies are more sensitive than my Santa Monica artist-type girlfriends.

You guys are great. Thanks a ton for the insider secrets. There should be a little counter near the nav bar that says something like "$XXX millions saved" from persistant potential parts changers like myself.

Thanks.

OK, ready for the next post?

Coming to the board near you immediately.

P.S. The transmission thing is still in question, but I think we'll drive it into a new post. Thanks again!ME