1992 Q45 stumbles, hesitation, rough idle AFTER warm up

[rdownings]

When cold, the engine is very smooth, acceleration is great. No problem.However, after the temp indicator show normal operating temp, the idle becomes rough and sometimes I get no power pressing on the gas, or I get a popping sound from the engine bay, or a bucking of the engine while at a cruising speed.

I checked for codes and came up with 12 and 33. I replaced the MAF with a tested good one, but not the other part yet. So code 33 is still there.

I thought maybe injector, fuel filter, plugs, or plug wires, but they would be bad no matter if a cold or warm engine.

I guess I need to know if this could be a problem happening with air intake after warm up, or a stuck valve? an electrical problem?

I cleaned the TB and checked connections to the MAF and the TB. Any other ideas? Oh, plugs and wires are new.

Thanks

[maxnix]

New wires? There are none. Hope plugs are NGK OEM specification.

How about the fuel pump? Might spend some time reading Articles before reading all previous posts by Q45tech.

Do you have the revised chain guides? What is the dealer performed service history?

[Rex]

Welcome to NICO.

The Q45's motor (VH45DE) does not have plug wires, as there are coil packs on each plug.

A few things you'll want to research here via articles and the search function are- Chain Guides (90-93 were plastic backed and will fail, casuing timing to jump and motor to "lunch")- Injectors (especially with you being in Cali)- transmission cooler- Fuel Pump- OEM plugs

That should get you started and keep you busy.

We're all very willing to help, but it will all make more sense if you've read some of the information that has already been discussed. I hope you have the dealer records of maintenance, that's always helpful.

[rdownings]

Hi, Thanks for the replies so far.I am mistaken about wires. I replaced wires and MAF on my 300zx and the MAF on the Q at the same time. I was writing my post late at night, so duh on my information. Sorry about that.

Anyway, the Q has been sitting up a long time before I got it. The dealer had it sitting in their back lot, I saw it and gave them 2k. No service history. They said they changed the plugs before I picked up the car, so I am taking their word on it.

Regarding the fuel pump: It is noisy and I read that this could be an early sign of pump failure. I did add Techron to half a tank of gas.

Don't know about the chain guides either. No service history in the dealer database.

But I guess my post is questioning why does the car run badly after it has warmed up? It seems that the issues mentioned would be present during warm up time as well.

This is the 3rd Q45 I've owned and it never had problems with the first two (1990 and 1992). This is why I am new to the forum.

Anyway, I will check the articles and the advice given so far.I really appreciate your responses and look forward to reading everything.

Thanks,Rick

[maxnix]

1.) No service history.

2.) They said they changed the plugs before I picked up the car, so I am taking their word on it.

3.) Regarding the fuel pump: It is noisy and I read that this could be an early sign of pump failure. I did add Techron to half a tank of gas.

4.) Don't know about the chain guides either. No service history in the dealer database.

1.) Call Infiniti Customer Service and register the car. They can pull the history form the archives.

2.) Don't believe them for a NY minute. Why would they? May have used wrong plugs even if they did.

3.) Too late for Techron, which won't help an expired fuel pump.

4.) Assume they are failing and at least one piece is in your sump.

Don't drive your car until you do a lot of reading here and have a strategy to repair the imperative and get it back on the road.

[SOCAL91Q45a]

Similar running problems for me the other day. Affter the drive home from replacing the O2 sensors - card would barely run .. felt sounded super rich ... coughing ruff idle sputtering ...

Well - we had bumped an egr tube off connecting the O2 harness .... Duoooh!

[pretzelboy]

You could save yourself alot of headaches and buy my 94/132k for $3800.....just had it detailed...knock sensors done-water pump...runs great....yes, the passenger side valve cover leaks---but after changing to 10/40 I think its almost a non issue(no dripping on the ground).....I'm in Huntington beach.......email me for pics... [email protected]

[rdownings]

Hey Socal91Q45a,I have done those (Duoooh!) things with other cars I've owned.

I forgot to mention in my post that my problem is intermittent. It comes and goes when driving. It is not a steady problem.

Also, I stated that the car runs fine when cold in the morning. The intermittent hesitation, sputtering, and rough idle happens after the car warms up.

My Z had a bad EGR and gave me the same symptoms as the Q. I wonder...

But I am in the process of investigating all the things others told me to look for.

[maxnix]

Tried ISO-Heet yet? Lot of rain out there recently can lead to condensation in the tank or infiltration into underground storage tanks.

[rdownings]

Hey,Did not think to try ISO-Heet. I was driving the car this morning and no problems. I stopped somewhere started up and drove and the hesitation, poor idle, and bucking at cruise came back. The car never dies on me.

In case anyone wonders, I only get a 33 code (exhaust gas sensor, left bank) from diagnostics. Service Manual says check Harness, the sensor itself, fuel pressure, injectors, intake air leak. Hmmm...will do this today.

[DAEDALUS]

Too rich (O2) or too lean (pump). If they're original, replace both sensors.

[3Q Jay]

missed your post earlier. since no one else spoke up about code 33 [although most have suggested the O2's], I'll confirm that code 33 is for the oxygen sensor.

[Jberger]

Having a very similar problem myself. The fuel pump was REALLY loud so I just got finished replacing it. Checked the FPCU, it's in perfect order, looked factory fresh. The new fuel pump has made the problem MUCH worse. It's gone from intermittant when warm to completely stalling out after 4-5 minutes.

I think it's at least 1-2 injectors. They seem to be failing when warm and I think the new pump has much more pressure, so it's flooding and causing the problem.

I've got to head out and buy a new meter since my trust Fluke has been giving me trouble. Might wanna check those injectors!