Stalling when warm

[dave00092]

Hi, I am new to the board (THX mannix!). I have a '90 Q45, when it warms up (and the temp gauge hovers at mid point) --- it tends to stall, infact die. Once I resart, the problem seems to go away. So here is what I have done to date: 1) added one can of fuel injector cleaner to the gas; 2) replaced fule filter in engine compartment; 3) cleaned the throttle body with TB Solvent; 4) cleaned MAF with electonic contact cleaner. This has helped a little' --- but it still stumbles and dies, after about 10 miles of moderate driving. Any suggestions on the next diagnostic step(s) Thanks, Dave
Modified by dave00092 at 7:36 AM 7/31/2005

[maxnix]

Dave welcome. Might be better if this post was in the Infiniti Mechanic Forum, so don't be surprised if it is moved.

A little maintenance history might help them. Like did you clean the IAC and EGR valves and replace the PCV valve? Is the fuel pump noisy? Was the FI cleaner Techron or BG44K? How many miles?

Oh, by the way, if you haven't done the timing chain guides yet, you need to get to the Infiniti Articles and read that one.

Try a search in the post bodies of this forum and the Infiniti mechanics Forum for stumbling and stalling, both current and archived.

[dave00092]

I put one pint of "SeaFoam" --- in the gas tank, upon the suggestion of Napa (in the past I have used Techron). The next day the stalling got a lot worse, my specualtion is the Seafoam was too agressive and dislogged some debis or buildup --- which went upstream. The other steps I took reverted me back to the original condition. I need to go through the other steps you mention.

[elwesso]

I think your probably experiencing MAF failure...

[elwesso]

Just so you know, I took your thread from infiniti general, merged it with the one in online mechanic and deleted the duplicate post!

[96Qowner]

I agree with Wes. I consider myself somewhat of a MAF expert on this forum, since I stubbornly lived with a bad one for 15 thousand miles over more than a year. I wanted to isolate all the symptoms and try everything. I must have cleaned it 6 or 7 times over that period. It would work well for awhile, over steadily decreasing periods of time.

You should also be experiencing stumbling/coughing/bucking, if it's the MAF. Like you, I found that it tended to misbehave most after a short warm soak, like stopping on the highway for gas for a few minutes and getting back on the road. Then, during the first few minutes at speed, or while first accelerating, it would cough and buck a bit before settling in. When it was particularly bad, it would also stall and die when coasting to a stop.

The best solution is simply to replace it with a used or new one. A few of us have bought used replacements through car-part.com for $35 to $75 and they've worked fine. 90-94 have a common connector, 95-96 have a different style.

It seems the connector is the first problem area. Apparently, the circuit that burns contaminants off the MAF element fails, and crap builds up on it. Often, just replacing that will solve the problem - many dealerships have simply replaced the connector and that has fixed the problem for awhile. If not replaced early, the MAF itself goes bad. Try wiggling it while the engine idles to see if that's the issue. You might also try giving the connector contacts a good cleaning - both ends. The contacts on the MAF end are recessed and hard to get at, but you can get in there with a narrow knife point and scrape off any corrosion. Apply some dielectric grease and snap it back together. Like the MAF cleaning, if this makes things better, you've probably isolated the MAF as the problem.

But you'll probably have to replace the MAF soon, anyway. My experience taught me that there really isn't a final fix, other than replacement. At $75 or less, it's cheap enough that it really isn't worth messing with repeated cleaning and fiddling.

[dave00092]

Thank you all for the suggestions! Dave

[maddieQ]

hi Dave,

I'm having similar issues with my Q 45 94. Let me know if you were able to solve it. Still searching for the elusive MAF

-M

[dave00092]

Here is what I found with my MAF: I cleaned both the senosr wires and connection with electical cleaner. The connector was corroded (greenish) so I used a copper cleaner on both sides. Upon restarting, the car ran 'better' but still dies whan warm --- after 10 minutes or so of driving. I still need to go through the PCV and EGR cleaning. Also, I am thinking of changing my thermostat --- as in traffic the temp gauge goes up to H. Maybe in fact its a cooling related issue.

[Jesda]

Check your injectors as well. Perhaps when its getting hot its affecting the injector coils. However, I very strongly lean toward a MAF problem, which can also be more prevalent in hot weather.

Regarding your cooling issues, make sure you have a new t-stat, two new caps, and if possible, have it removed and cored by a radiator shop. I assume you still have the OEM radiator with metal end tanks.

[OvrKill]

Well it looks like I posted in the wrong forum to begin with. I have read a lot about the fuel pump issue and started to think that might be my problem, but now that I read a little about the MAF I think that might have something to do with it.

My car sputters and dies when coasting to a stop and I have to keep my foot on the gas at idle otherwise it will die. I am also pretty sure I have a leaky injector (hard to start after sitting for a little bit after an extended drive) I am at a loss I see a possibility that it could be related to all 3 of these problems.

I am going to go out this morning and listen to the fuel pump to see if I can hear a hum, and I am also going to check the MAF connection to see if that will effect it any. If anyone has any ideas I would appreciate it.

[maxnix]

Good start. Report back, but don't drive until the coolant problem is cured.

Overheats fry the KS, at best. Kill engine, at worst, which is more frequent than should be.
Modified by maxnix at 11:45 AM 7/30/2005

[Jesda]

Wes has an excellent writeup on how to easily check your injectors:http://www.q45.org/ohminjectors.htmlMake sure you remove the key from the ignition and turn off all accessories when you do it.

Checking your injectors should at least rule out injector coil failure, but the method won't verify leaks or bad seals.

If an injector was constantly leaking and causing the car to run rich, you might see a puff of darkish smoke from the exhaust at idle or a strong odor of gasoline. Note that its normal to see a light puff when first starting up, since the ECU sends a command to deliver extra fuel at startup.

The more you describe the problem, the more I suspect the MAF. The best way to keep the MAF from going bad is to use Nissan/Infiniti air filters and replace them per the owner's manual. According to "texasoil" (NICO member, active suspension expert) a bad or poorly installed filter will allow excess particles of dust and sand to hit the very fragile sensor element at a high velocity, slowly causing damage and incorrect readings.

Another quick thing to check... remove the plug from the fuel pump control unit in the trunk (right above the fuel pump, mounted to the bottom of the rear deck). See if a wire connector looks burned or black. If it is, your FPCU might be on the brink of failure, causing idle and driveability problems.

Sorry if you've heard all this before, I'm just covering the bases.

[dave00092]

Hi, Thanks for the tips. I'll check those points out.

...it almost seems that I have an idle adjustmet problem --- that is whaen the car is cold it idles at about 750 rpm, but once it warms up fully, it drops to 500 and runs a little rough.

It die when you get off the gas --- at about 45 mph. Like when you come to a light.

It 'stumbles a couple of times, the tach drops form say 1200 to 500 --- and dies.

When I go top resart it fires right up.

I was thinking about setting the idle up. What I see are two similar and (maybe related) set screws:

a) one on th etop side of the throttle body that is defintely a stop --- for basic idle and;

b) one 'below and behind' the large spring --- it seesm to be hooked to a 'dashpot' (circular body about 2 inch diameter), looks like a vacuum control --- in the old days I would have thought this was a vacuum control for deceleration.

In any case, i am relucatant to fiddle with 'b'.

Any suggestions?

[Q45tech]

Study how the IAC works in deceleration and steps up to supply a sufficient quanty of air to not stall with a sudden closing of throttle as your speed increases and steps down as you coast down to a stop.

Study the mechanical [coolant temperature controlled-----hot wax cold wax] fast idle warm up system used to take the load off IAC [so it [IAC]doesn't have to operate at 100% wide open while engine warms up.

Instead the warm up system lifts the throttle plate open a tiny decreasing amount as the coolant warms up. [1500 rpm>1300> 1100>900>750]

Throttle body dirt, IAC dirt, Maf dirt...............dirt everywhere [inside and out] is the typical Q we see.

ONCE everything is clean enough to operate with on a family member, then you deal with electrical and contact corrosion..........sending intermintent errors to ecu

[RobertsnewQ]

Study how the IAC works in deceleration and steps up to supply a sufficient quanty of air to not stall with a sudden closing of throttle as your speed increases and steps down as you coast down to a stop.

Study the mechanical [coolant temperature controlled-----hot wax cold wax] fast idle warm up system used to take the load off IAC [so it [IAC]doesn't have to operate at 100% wide open while engine warms up.

Instead the warm up system lifts the throttle plate open a tiny decreasing amount as the coolant warms up. [1500 rpm>1300> 1100>900>750]

Throttle body dirt, IAC dirt, Maf dirt...............dirt everywhere [inside and out] is the typical Q we see.

ONCE everything is clean enough to operate with on a family member, then you deal with electrical and contact corrosion..........sending intermintent errors to ecu

I can relate to that with my experience. WHen I got my car the idle was about right, but somewhat rough. After cleaning and replacing all the plenum hoses and gaskets and without adjusting the IAC it idled at around 1000 rpm warm! It turns out the previous mechanics had increased the IAC screw until it was 4-5 turns out. Now it idles perfectly at 2.5 turns out, like it should. The moral of the story? Clean the MAF sensor and its electrical connector (use dilectric grease), the throttle body and throttle plate, and as much of the plenum as you can reach. Then adjust the IAC 2.5 turns out and you should be pretty close to accurate...