99 Alty idle problem, pls help!

[merc68k]

Hi guys, just joined the forum, looks like a great place to learn a lot of great tips and tricks!

I've got a question as my first post, about my 99 Altima GXE (5 speed). I've had it about 16 months and the idle has always been too high. I had a 1994 5 speed before this one, so I know more or less what to expect as far as the idle and idle behavior goes.

The first thing I tried to do when I got it was turn the idle adjust screw, but I couldn't get the damn thing to turn for the life of me, and ended up destroying the head on the screw (it was already pretty rough before I finished it off).

Are the idle adjust screws typically hard to turn like this? What I'm wondering is, if the screw is sealed from the factory, and mine hasn't ever turned, then maybe something else is causing the idle problem.

I've had it to the dealer, where they checked the TPS adjustment, timing, and anything else they figured was relevant, and everything tested ok. I had already tested the TPS and timing myself and they seemed ok according to the service manual.

The idle is typically around the 850-950 mark. That on its own wouldn't be so bad, but the other issue is that anytime I put the clutch in when I'm coming to a stop, especially before the car is warmed up, the revs will run up to 1500 rpm or so and hang there for a few seconds. This makes smooth starts without a lot of slipping clutch hard. Also anytime I touch the gas pedal, the same thing happens with the revs going up for a few seconds, after I have released the gas.

I have messed around and been able to improve it by installing a restrictor (rubber washer from a sink faucet) in the rubber hose that runs to the IACV, but that brought its own issues. I also adjusted the throttle stop screw, which brought the idle down and more or less stopped the revving up at stops, but didn't affect it when the car was cold thanks to the fast idle cam keeping the throttle open until the engine warmed up.

Anyway, I think the issue is that there is just too much air getting into the engine at idle, whether it's simply due to a misadjusted idle screw, or a vacuum leak somewhere, or something else.

I tried disconnecting and plugging the rubber hose to the IACV while the car was running once, to see if it would continue to run, which would mean it was getting air at idle from somewhere else, but it stalled out pretty quickly so if there is any kind of a vacuum leak it must be pretty small.

I'd like to be able to replace the idle air screw, or the little plenum that it screws into along with the IACV and FICD valve, does anyone know if that part is available on its own?

Failing that, has anyone else ever run into this issue? It's bugging the hell out of me and it would make my day, week, and month if I could figure it out!

Thanks in advance!

[NISTECH]

The best way: Go out and buy a cheap digital volt meter. Hook it to your O2 signal wire and moniter your o2 voltage at idle. Should fluctuate a bit. If it just stays locked on 0.00v you are running very lean. This typically indicates a vaccum leak. If you find this the case. Spray some brake clean or carb clean near the lower edge of the #4 intake runner where it meets the head. Get the spray as close as you can to the mating surfaces of the intake and head at the bottom. While doing this watch your volt meter. If it jumps up to ~.8 v and hangs for a few seconds you have found your problem. It would be the bottom of the intake gasket got sucked in a bit at the bottom. I have done many of the altimas for that exact problem.

Alternatly: you could just spray there and listen carfully for an RPM change with the engine. Sometimes it works sometimes it doesnt.

I am concerned with you idle adjustment screw issue though. The screw is straight down between the #1 and #2 cyl intake runners,this is the screw your trying to turn right? I cant recall ever seeing one that had a problem turning. Any of the screws on your throttle body are intended for part calibration of the throttle body components during manufacturing. They are not adjustments. By moving them you are changing the calibration of the throttle plte to body clearance. You risk having a binding in the future or damaging wear to the throttle body surface by changing that calibration.

[merc68k]

@NISTECH

Thanks for the reply. I do have a DMM but haven't tried monitoring the O2 sensor yet. I tried the diagnostic mode in the ECU that flashes the CEL x number of times while the car is running, to indicate how the sensor is performing, and I forget the details now, but I think if it blinks at least 5 times in 10 seconds, it's good... mine was well within the norm.

I will try to spray some TB cleaner around the manifold gasket and see if anything interesting happens though. This car has a slight hesitation when I punch the gas at idle that my 94 didn't have, and I've often wondered if this is due to a vacuum leak or tied in with the idle somehow.

As for the idle screw, what I tried to turn is between the #1 and #2 (assuming #1 is at the timing chain end of the engine) intake runners and is set inside a threaded hole. It's right above the IAC valve and the IAC, FIC valve and the screw are all part of a piece that bolts onto the end of the bottom half of the intake manifold.

I know I wasn't supposed to adjust the throttle stop; it says it in big bold letters in more than one place in my manual, but I marked where it was before I turned it, and only turned it out about 1/4 turn. It's back to where it was originally now.

[NISTECH]

Wow I have never seen those screw get stuck like that. You got the right screw though. All that comes as part of the IACV assembly. That in itself is a royal pain to replace. If you do find an intake leak where I stated you would be wise to replace the IACV while you have the intake manifold off. Hint: dont seperate the upper intake from the lower. Its easier to pull it out as one piece. Its the intake to head screws that are a real pain to get out especially the one near the IACV. I use a 12 mm 1/4 inch wobbly socket with 3 inch extension to break it loose and get it about half way out. Then I remove it the rest of the way with a box end wrench.

[merc68k]

Yeah it really seems to be stuck in there . I actually managed to get all 4 (are there more than 4?) bolts that hold that whole assembly in, out this past summer. But, it wouldn't budge from the manifold, and I wasn't sure if there was anything else holding it on there so I didn't want to force it too much.I'm not sure if I would have enough clearance to even get it out of there with everything still in the car either. If I could get it out though, I might have a chance at freeing up the screw.

I can't get any screwdriver in at quite the right angle either, so it's never quite squarely into the head of the screw, which doesn't help... I wonder if I could get my hands on the right stripped screw remover if I would have any better luck.

[NISTECH]

It should be a straight shot into the screw from up top?? There should be no obstructions?

Yea once those 4 screws are out you give it a light tap with a hammer and comes free from the manifold. You take it out through the bottom of the car.

[merc68k]

Yeah it's nearly straight down, but I never could get it straight on... maybe just a matter of not having quite the right shape screwdriver. Maybe if all else fails, I'll take another crack at hauling that whole part off of there and see if I can get that screw freed up somehow, or just replace it.

Thanks for the replies, I'll post back with any results when I get em...