92 Q: oscillating idle suddenly

[kdkrone]

92 Q45 with 97K miles, new plugs and injectors within the past 12-14K miles. For the past two days, the yellow engine light has come on while driving (the first two times) and then went off after about 10 minutes. There was no engine miss. This AM, the light was on and there was a missing while the engine warmed up but after the car was warm, I stopped the engine. When I started it again, the idle oscillated between about 200 and 1200 RPM, then settled down to 600-700. I stopped the engine again and the same thing happened.

I am about 2 1/2 hours from where I live and am wondering what the problem(s) might be. There is no Infiniti dealer here to service it, although there is a Nissan dealer.

Thanks for your best guesses,Ken K

[96Qowner]

Have you noticed any missing, or coughing, while driving? The connector on the MAF, or the MAF itself, may be misbehaving. You should start it up and fiddle with the connector plug. If so, you can try cleaning the connector pins and treating them with dialectric grease. (The Mass Airflow Sensor is the square box on the big hose between the air filter and the engine.)

If it's the MAF, it won't strand you, though - should be able to get home. If you have the time, do a search in the archives for MAF.

EDIT: I checked your posting history and see that you've dealt with the MAF before as well as a really unfortunate history with bad injectors.

[kdkrone]

Hi. Thanks for your post. I will check the MAF later today. While I certainly had my problems with the injectors, about 12-15K ago, all have been replaced (thanks to California gas), and what is happening now doesn't seem to be the same as what had been the problem in the past. The suggestions about the MAF in the past never panned out--the situation was solved by changing out the injectors-but at least I learned where the MAF lives!

I have not noticed that there has been any coughing or sputtering other than when I first started up this AM and it was cold (40's). Within a block, it was gone.

ThanksKen K

[texasoil]

The symptom points to either a sticking idle control valve or an electrical problem caused by moisture possibly. A coil could be going, a spark plug, or just a faulty electrical connection. I am a BIG proponent of Stabilant-22 (CL-85 is Borg Warner name) for use on ALL Q45 electrical connectors. They are very good electrical connectors--but time and environment does make itself known. A thin,invisible film of corrosion forms over time, and then if the connection is ever moved-it will not re-make a good as new connection. Even brand new-just manufactured connectors--even gold plated very costly computer/space grade ones IMMEDIATELY pick up dirt and corrosion. Extensive testing has proven that Stabilant -22 is THE CURE, THE MAGIC POTION for ensuring 100% electrical connections. Demonstrated DRAMATIC improvement in connection quality with even brand new just made mil-spec computer board edge connections! We just have been thinking we had good connection, when what we have is usually just OK/marginal. The Q45 is VERY sensitive to poor quality connections since there is a lot of low current, low voltage signaling going on in the car area LAN.

While it does cost about $58 for the 10ml size bottle--that is a 'lifetime supply'-since you swab only a tiny amount on the contact surface. I can personally attest to its effectiveness. I have found than many 'electrical system guru's have it stashed away in their secret bag of know-how. High end video and audio shops now carry it also.Every IBM computer maintenance tech has it on him, and most military electronics/avionics specialists have it in their kits too.

[kdkrone]

Well, the talk about the electrical connections is of interest, as I had an oil change last weekend during which they checked my air filter. I will have to check the MAF connection; it may be the culprit.

I appreciate the info about Stabilant -22 .

Ken K

[kdkrone]

By the way, do you have a source for Stabilant-22?

KK

[kdkrone]

Well, last night before I took off for a friend's house, I had little time, so I just played with the connector to the MAF. The Check Engine light came on when I started and turned off about 5 mintues later. It did not reappear on the 8 mile trip back from my friend's house nor on the 15 mile trip to work this AM. So far so good.

Before the light went off, I put the car in neutral and the idle varied between 1200 and 200 a few times before settling down. After the light went off, it was normal.

MAF??

ThanksKen K

[96Qowner]

Deal with the MAF connector first. If the connector is the issue, you should be able to start the engine and wiggle it and see the idle change.

Here's Texasoil's thead on Stabilant-22:

zerothread?id=151455

Of course, sometimes the MAF problem is deteriorated connections INSIDE the housing, where you can't get at them. The solution then is a used replacement through http://www.car-part.com for about $75 or a new one for mid $300s.

[kdkrone]

So with prices for an MAF varying from $250 and less, how does one do the selection for a used part??? (assuming that I would need one...)

KK

[goody90q45]

Buying from an established NICO member, not a one post Newbie, selling one in the infiniti parts forum would be your best bet. For the most part everyone is pretty up front about the condition of the parts they are selling. I've had nothing but good experiences and good prices from everyone I've dealt with here. There's other internet used parts stores out there but I have no personal experience dealing with them.

[96Qowner]

A few of us have bought MAFs through car-part.com and had no trouble at all. It's just a clearinghouse for parts dealers. Presumably, the MAFs were working fine when the car was scrapped.

Of course, getting one from a NICO member would be assured.

Some will insist that a MAF is a wear item and should be replaced with new, but with that kind of price differential you can buy quite a few $75 used ones. Plus, the replacement is a simple 5 minute thing - no real labor.

[Q45tech]

Be sure to check them with a consult or a Hi low peak hold VOM as We see a few that are in accurate..........the failure mode is too much output voltage for the amount of air flow.

One example read fine at idle but progressively over estimated the air flow close enough at cruise for O2 to trim out correctly but at wide open throttle above 4,000 rpm became 20-30% too rich........more than normal black smoke and lost power from way too much fuel............instead of an expected 11>10 ms it read 12>13 ms..................this was only a few tenths of a volt higher 4.3 >4.5 volts............the exponential curve of the MAF voltage.

Every dealer in town misdiagnosed this one............you must know what is normal and what is not and be exacting in your measurements.

Most failures are more noticeable but you must be prepared for the occasional sutble ones.

[kdkrone]

q45tech,

While I do not completely understand what you have said and I do not have the equipment to check things out, I do recall that the other night when the light was on and I got out of the car after stopping the engine, that there was a smell of fuel in whatever exhaust fumes were around the tailpipe. I have noticed that during the past two days while the light was NOT on that the fuel smell is no longer there, so I think that folks here are pretty correct about the MAF. As it cleared up after I played with the connector, that tends to confirm it. If anything else happens, however, I will be back here!

Thanks to all for the help, Ken K

[kdkrone]

Follow-up. Since cleaning the contacts of the connector for the MAF with Stabilant 22, I have had no further trouble.

Thanks, allKen K

[3Q Jay]

cool. where did you source the stabilant 22? need to get over to kragen and see if they have it....

[maxnix]

I had an oil change last weekend during which they checked my air filter.

If they went at the oil filter from the top, a real red flag for the MAF connector!

Always examine the quality of the connection to each plug first before replacing MAF.

[kdkrone]

Re: source for StabilantThis is where I purchased it. There are probably other places. I don't think you will find it at auto parts stores.

https://www.micro-tools.com/store/mainframe2.aspx

[kdkrone]

RE: oil filter change. They went after it from the bottom. They did, however, check the air filter and probably disturbed the contacts at that time.

KenK

[Aussie VH41]

My 1992 VH41 has the same oscillating idling problem + hesitation using small throttle opens + rough idling and replacing air filters & plugs did not fix it. Then, I read this thread and Q45.org and gave me a few more things to check. Cleaning (and 2 more re-cleanings) the MAF made the problem spread to now not revving above 2000 rpm and very small backfire when hesitating.

Next, I used injector clean which fixed the revving and backfiring problem but the engine revs in the 1600 rpm when cold to warm (drops to 800 when normal) and the hesitation problem has been reduced but the rough idling comes and goes. I will run it for a while then do “The Plenum Job� as per Q45.org if it does not improve.

Thanks for posting this info as it has been a great help.

Paul H.

[kdkrone]

Aussie VH41,

I would strongly suggest following up with the solution to clean the electrical contacts of the connector. At least for me it did the trick.

Ken K

[Aussie VH41]

It fixed for 4 days and counting. I pulled the plenum off to check the injectors/cleaning and found 1 of the 'O' rings to be 'hard'. When re-assembling this ring sucked air, off with the plenum and used gasket goo on all eight rings.

Runs like magic again and the temp gauge dropped 10 degrees Celsius and the fuel economy is back to 12lts/100k.

Thanks again for all your help..

Could not find Stabilant in Aussie so I used Dia-electric grease..

Enjoy

[3Q Jay]

The symptom points to either a sticking idle control valve or an electrical problem caused by moisture possibly.

just want to give Keith a plug here.....this nugget of info on sticking IAC is probably overlooked a lot. even after cleaning, it seems that the stickyness can still be there. especially noticable when at hot idle...i was chasing this gremlin for a long while. one way to check is to tweak the iac bypass setting just a bit and see if the oscillation changes as the ecu/iac duty cycle changes. i know tech recommneds a 10-15% iac duty at idle. since most of us don't have the consult, i set mine so that the idle is about 50 rpm less (yeh, yeh uncalibrated visual on dash tach--so what) with ecu control disabled in park hot no lights or a/c-- than with ecu control. then by minute <1/16 turns of the bypass screw set up where the hot idle restart does not fluctuate much.