2001 QX4 Idle problems

[lburton]

has anybody encountered this.... while at a light or stopped while in drive, my suv will idle at around 800rpm then will start dipping to then jump back up. this morning it dropped real low to the point that it almost cut off. This happens frequently. it has 175k on it with latest maintenance done of it was the replacing of all coil packs back 1-1/2 years ago. Any help will be appreciated!

[goody90q45]

Is the check engine light (CEL) on? When this happens in a Q45 it's usually 1) a failing Mass Air Flow Sensor (MAF) or 2) the MAF and/or its connector have corrosion or 3) the female pins in the connector are loose. Clean and tighten the pins first and see if that helps. If corrosion is present lube with dielectric grease.

If no CEL than you could have a fuel pump going bad. Any acceleration problems or issues other than at idle?

[lburton]

no CEL light cut on. Well as far as acceleration/ idling problems go, seems to be mainly noticed while sitting in drive. driving seems to be fine except if I accelerate hard on it, it has problems catching gear.....normal driving, it shifts fine but that’s a separate issue.

I've had this suv since 03 and now I’m trying to tackle past issues and maintain the maintenance on it.

[lburton]

From reading other posts about the same issue, it was suggested to be the MAF like you said. I'm probably going to tackle that first and go from there. I'm sure it needs it so it wouldnt hurt either way. I've taken it to Nalley Infiniti here in ATL. for maintanence and for the replacement of my coil packs ($$$) but now its time to tackle issues myself and save the markup and labor cost. Will say they have been pretty good to me and the vehicle! I'm pretty handy just in the past i didnt have the time. plus it was always nice taking the g37 out as a loaner!!!

[goody90q45]

no CEL light cut on. Well as far as acceleration/ idling problems go, seems to be mainly noticed while sitting in drive. driving seems to be fine except if I accelerate hard on it, it has problems catching gear.....normal driving, it shifts fine but that’s a separate issue......

With no CEL light you may want to measure fuel pressure after the MAF connector is cleaned up. Can you hear the fuel pump running when sitting at idle...it sounds like a swarm of bees when it's failing. It's cheaper to buy a pressure check kit ($30-$40) and DIY rather than take it to a shop. Easy stuff, tee in past the fuel filter.

[goody90q45]

From reading other posts about the same issue, it was suggested to be the MAF like you said. I'm probably going to tackle that first and go from there. I'm sure it needs it so it wouldnt hurt either way......

More easy stuff. A toothbrush and penetrant (i.e. PB blaster) to clean the connector, a small finishing nail to tighten the pins, and a small brush to apply the dielectric grease when you're done. You'll be done in 5 minutes. If it doesn't help buy a can of MAF sensor cleaner and spray clean the MAF filament and its internal surfaces. Tell us you're not running with an oiled filter or cone filter?

[CanuckQx4]

Tell us you're not running with an oiled filter or cone filter?

[lburton]

I have a K&N drop filter which I had for 5 years if that answers that question. And yes I maintain it with the K&N cleaner kit.

[goody90q45]

Chances are the MAF filament is dirty from the oiled air filter. Clean it with the spray cleaner and consider changing back to a standard air filter.

[CanuckQx4]

Why would a non oiled, but aftermarket cone filter from K&N be a problem?

[goody90q45]

There's nothing wrong with using a K&N filter or a cone filter but the OP said that he/she follows the filter cleaning schedule which implies that the filter was oiled. If it was oiled the MAF filament certainly has a coating on it which would make it hard to function properly. Clean the filament with MAF sensor spray cleaner and it should run better.

[CanuckQx4]

Id like to do both things you mentioned in this thread, check fuel pressure and tighten my MAF connectors. How do you do that with a finishing nail??

Also do you happen to know the proper fuel pressure??

Im having some full throttle problems aswell, shifts fine under daily druising, but has no power at full throttle. Ive done a full tune up and now a new MAF and still have this problem.

Ruling out fuel and loose maf would be nice. And I happen to have a spare fuel pressure gauge and fuel line so I can make a T easy and leave it under the car if the pressure only needs to be tested at idle

I think I owe you some $$$ with all this help Im asking from you Goody lol

I appreciate it alot, Id love to have a nice running Qx4 and concentrate on school again instead of always having this on my mind

[goody90q45]

Your QX4 is probably not going to have the same connector but the idea is the same. If the MAF connector has play when connected it may need to have the pins tightened to look like the one in the middle in the pic. Also clean up any corrosion on the connector pins and MAF pins and lube with dielectric grease.



Unless you purchased it new, clean the MAF with a can of spray cleaner for MAF sensors. Remove the MAF and use the whole can concentrating on the sensing filament. Let the MAF dry in a warm place for a bit before reinstalling.

To check fuel pressure, tee in with your gauge on the fuel inlet hose close to the intake plenum. Pressure at idle S/B close to 34psi and 40+psi at full throttle.

.....I think I owe you some $$$ with all this help Im asking from you Goody lol......

I'm happy to help. It's payback for all the great help I got as a new Q45 owner. It's what NICO is here for.

First priority should be to get that capped off vacuum hose reconnected in the proper location. Are there any other QX4 owners close so that you could take a look at their engine compartment?

[CanuckQx4]

I did change all my vacuum lines today, followed the FSM best I could, look how bad my oem ones were!



I also tightenned the MAF pins thank you very much for that diagram, I thought there was a set screw to tighten them after hearing you say that, but that makes alot of sence, they were fairly tight, but they are tight as heck now

I also borrowed my dads fuel pressure gauge and I plan on T-ing it into the fuel line tomorrow, no store were open with 1/8" npt -> barb fittings. Would it be fine if I spliced it in right here? Im unsure if this is a good spot or not. You mentionned after the fuel filter which is very accessible at the back of the car, or I can splice it in here under the hood.





I think fuel pump is a very good possibility of why I may not be able to go full throttle and get the power I used to have, it seems to just stop accelerating past 4k rpm, very slowly anyways. engine seems to be screaming like it wants to go, but the power just isnt there. Would be nice to know if I have fuel pressure or not

[CanuckQx4]

And do I need to monitor the gauge when driving?? if so I would need to pickup a decent length of hose to mount the gauge in view of the front windshield while driving to see if I have pressure at full throttle,

I havent drivin the car yet since replacing all the vacuum lines so I dont know if it cured P1110 yet, but I hope so!!

The car threw P1165 and P1110 on my way to home depot/rona to check for the barb fittings, but I hadent changed the vacuum hoses before that drive.

Im really willing to do ANYTHING to get this car running good, strong and powerful again. This is killing me mentally lol, thanks again

[CanuckQx4]

bump, Id really like to utilize this gauge and check fuel pressure, is there possibly a better place to tap into for its connection??? Or is the place I posted in the picture suitable??

I dont know off hand if that is a return or a feed

[goody90q45]

Where you have it in the pic is good- close to the engine. When I said after the fuel filter I was thinking about the Q45 which has it's fuel filter in the engine compartment.

Look at the fuel lines closely to figure out which is supply and which is return. By feel, with the engine running, the supply line should be hard since it has 30-40 psi and the return line should collapse when squeezed since it's open to the fuel tank. You still need to verify visually. No need to monitor while driving. The fuel pressure will change by opening and closing the throttle plate manually from the engine compartment.

[CanuckQx4]

Ok I hope it helps, I think I may have a fuel problem, Ive been having a startup issue where my car will crank for 4 seconds or so before it kicks over, but its much faster if I turn the key to ON first and let it prime I guess.

So Id like to check fuel pressure

I'll do the hose collapse test to make sure Im dealing with the feed. thanks for the tip on finding that