Alright, here's the sitch... symptoms first, then backstory (skip the last paragraph if you don't care):

My car used to stick at around 1500 rpm for a while when cold, and then gradually come down to normal speed as it warmed up (normal). It would also stick at 1500 rpm momentarily after coming to a stop while driving, and then come down after a few seconds. I figured that was normal behavior, or attributable to my still having an auto ECU after my 5spd swap.

Now, it sticks around 2000 rpm every time I start it -- cold or warm. On cold mornings, if I let it sit for a while to warm up, after a couple of minutes it will drop down to 1500 and then immediately bounce back up... and keep cycling up and down like that every few seconds until I get moving. After I start driving, every time I put the clutch in or come to a stop in the first few minutes of driving, it sometimes jumps up between 2500 and 3000, and then slowly comes back down. Occasionally it will drop back down to 800-900 rpm if I let it sit and idle for a while, but it really, really likes to stick around 2000. I'm also noticing more-than-usual fluctuation when the fans and headlights turn on.

Now, the backstory....

After I got my polyurethane motor mounts installed, the regular engine noise when idling around 600-700 rpm would resonate like crazy in the cabin. No problems... I used the totally by-the-book method to adjust the idle up to 800 and all was well. Then I ripped apart my upper and lower IMs to clean them and do some other maintenance. After putting everything back together, and one incident involving one end of the upper IM gasket starting to get sucked into the intake runners (don't ask), the car is idling weird.

Any ideas??

 

Vaccuum leak - one of your IM gaskets is not seated properly/cracked or damaged. As an aside, also clean out the IACV.

 

Try spray some TB cleaner or starting fluid along the gaskets - if it's sucking air in from any part, you'll hear the engine note change.

 

That IACV is cleaner than I am right now.

Just tried the TB cleaner trick and got nothing.

Any other ideas?

 

I have had all of that happen to me! Including the motor mounts /peice of gasket missing/swapped fed spec lower manifold and cleaned everything... All except that egr pipe and what ever else is in there.

Sometimes I get an abnormal wiff of exhaust. Major loss of power. These problems with irregular idle started in april. Now max jerks, hesitates. Maybe its egr related...?

 

Could be. That "other maintenance" involved replacing the EGRC solenoid (with the green connector) cuz I was getting a code for it, but I didn't have the time or the ***** to try replacing the valve.... Now I'm not getting any codes for anything except my auto transmission, which hasn't really existed since my 5-speed swap.

Well... technically since I spun out and smashed it on a rock. But who's counting...

I have noticed the idle fluctuates as EGR flips on and off too. Weird.

In any event... In case it matters, I also put in a 300ZX fuel filter and changed the PCV valve. I'm gonna swap out my plugs tonite since it's about time to do that anyway. In the mean time, further suggestions are welcome.

 

I still think it's a vacuum leak - and the IM gaskets are the likely culprit.

You could try loosening/retightening the plenum bolts and see if that helps..

I don't know the details of your mishap with the gasket getting sucked into the runners... is there a link that I can read up on it - it might give me some more ideas.


Good luck.

 

I know I have no vaccum leaks. When I took of the IM I was missing about an inch or so of gasket that had to have fallen in. I have not got any codes for any of the syptoms either. PCV isn't the problem either. I cleaned the IM totally, 1 step colder plugs (NGK), replaced TPS, cleaned IACV, changed fuel filter, PCV, removed lower manifold w/ swirl valve and repaced with fed spec. Before these problems became really noticable I had my trans rebuilt and added a light flywheel ( Fidanza), also this is the time of swapping the motor mounts.
Boost gauge reads 20hg so vaccum is good

 

Well, as I said, I recently removed and cleaned my upper and lower IMs and TB (IACV had been cleaned a few weeks prior). My brother and I got that done as best we could and put everything back into place with new gaskets. Well, long story short, trying to torque the upper IM bolts down with a torque wrench mistakenly set to 20 lb-ft resulted in two broken bolts, both on the left side (it was really late at that point). I used a C-clamp to hold that end of the manifold in place and started calling stealerships for bolts the next day. That C-clamp barely lasted that long: it fell off, and that's how that one piece of the gasket got partially sucked into the runners.

Needless to say that was corrected post haste (junkyard + popularity of the 4th gen > all). The gasket was fine -- it hadn't broken or cracked or anything. It looked like I had just removed it from its packaging. I just re-seated it, put the bolts in, and went on my way.

 

i'm having the same problem that wasn't corrected by: cleaning the TB, IAC

replacing the pcv, air filter, fuel filter, spark plugs, all coils

BTW, it runs syn + techron at all times. No codes, Nothing that brought this on. I'm leaning towards ECT sensor + TPS at this point. But it may be MAP related as well. I just love playing "enee menee minee mo" with all of the god for saken sensors on this car

 

Ya, the upper IM gasket is thick rubber.. I replaced mine when I did my valve cover gasket at 120k, and the IM gasket was still in really good shape. I don't know what the lower-IM gasket looks like.

Perhaps you have air seeping by the PCV, EGR guide tube gaskets, TB gaskets or even the IACV gasket... depending on how much you had to dismantle to get the IMs off...

Does the behavior change once the car has warmed up fully or it is noticeably worse on really cold AM starts?

 

You can check the TPS and ECTS with a multimeter - no need to waste money replacing parts that aren't bad.

 

This is true, but I'm starting to lose faith in this method of troubleshooting on the max. At any rate, I'm intriuged by that last posted question about whether this is a cold start problem. Would like to hear more.

 

It really seems only to happen on cold starts; the colder it is, the worse it gets. Warm starts are fine.

Just replaced my plugs, BTW. I had Denso Iridiums in there, which have an ULTRA-fine tip and have to be replaced after ~30k-40k miles (despite conventional wisdom about iridium plugs). Now running NGK Iridiums. The car seems a little happier but I still got the bouncing idle for a minute or two after starting it up, even after it had only been sitting (in the cold with the hood up) for about 45 minutes.

I will try loosening and re-torquing the upper IM bolts tomorrow morning before work.

 

Sounds like a plan. The reason I asked about it being worse in the cold is as the engine warms up, sometimes the gaskets start to seal better as they get softer (warmer) and the engine parts expand ever-so-slightly, forming better seals and eliminating the air leak.

 

Yeah, I figured as much as well. For that reason I tried the TB cleaner trick again this morning. Didn't get anything this time either, so I'm assuming I'm pretty free of vacuum leaks.

I didn't get a chance to re-torque those upper IM bolts, but the car seemed much happier today. The RPMs did dip down to 1500 and then bounce back up to to 2000, but only once rather than repeatedly. It's also taking quite a lot longer to drop down to its warm-idle speed (i.e. almost until the end of my 30-40 min commute), but it eventually gets there.

Could it be injectors? Maybe I got some gunk in them in the process of what I was doing with the IM, and it's slowly coming out...

What about O2 sensors?

 

Check your ECU screw - make sure it's turned all the way counter-clockwise. Also, I know this may sound silly, but while the car is idling high, try pull up on the accelerator pedal - perhaps the cable is sticking and the TB butterfly-plate is sticking open. You can also try this directly with the throttle lever on the TB.

I don't think it's the injectors. I've read about O2 sensors causing slight idle issues, but nothing like what you are seeing.

It may also be the fast-idle cam on the IACV.


Did you try spraying the TB cleaner around the IACV hoses, EGR, and intake parts downstream of the MAF? basically any air that gets in downstream of the MAF is unmetered and can cause the symptoms you are having.

What intake do you have?

 

Checked that stuff on the TB. All is well there.

I sprayed around every single vacuum hose, fitting, and gasket that I could see, including the EGR stuff around the back.

I'm using the stock intake, minus everything before the airbox.

I might rip open the IACV tonight and check it again. I'd need a voltmeter to check the fast-idle cam though, wouldn't I?

 

Looks like you're doing the right things... I'm not sure exactly how to diagnose the fast-idle cam off the top of my head - but I know it's in the Haynes and will surely be in the FSM. Let me know if you need the instructions (I can get them to you tonight).

http://www.sears.com/sr/javasr/produ...id=03482082000

It's a great deal and a MUST HAVE, in your toolbox.

 

Holy crap... I had no idea I could get one that cheap. Order placed.

I have the FSM in PDF form at home I think. I'll take a look for the procedure there when I get home.

Thanks a ton for your help so far!

 

Cheers. It's much easier to help someone who is willing to put in some effort on their own.

 

Well, I haven't been able to check the FIC yet, but I did think of another possibility.

I'd upload a pic of what I'm talking about here but my ImageShack login isn't working. It's on page EM-7 of the FSM, in the upper left of the diagram. There's a C-shaped tube that's shown just to the right of the EGR tube that lets exhaust gas into the upper IM.

What is that tube? I kinda cracked it removing it, but all I had to replace it was a longer section of same-diameter tubing that didn't bend as well. It wasn't totally kinked or anything, and my engine wasn't acting like this immediately after the service so I pretty much just assumed it was okay. Could it be a cause/contributor?

EDIT: I should also mention that with my TPS disconnected (like when adjusting idle speed), my engine idles around 2500rpm. Shouldn't it only be a few hundred RPM above normal idle?

 

FIC I'm feeling slow - it's been a long day at work.

Took a quick look at that tube... assuming I am looking at the same part that you mention, it's definitely a vacuum line and a possible source of the problem.

Spray some TB cleaner around there and see if you notice anything... from the FSM pic, I can't tell what the top of the tube is connected to... is there another pic of this in the FSM?

Also, try fiddling with the tube while the car is idling and see if you notice any change in behavior.

I can't remember of the top of my head what your idle should be with the TPS disconnected... I thought it is supposed to idle high for a few seconds and then drop down to the 500rpm range...

 

FIC = Fast Idle Cam. I actually did tweak it a little tonight... let's see what happens tomorrow morning.

As far as I can tell, that tube is impossible to get to with the IM and everything in place.

I heard that with the TPS disconnected, it's supposed to idle a few hundred RPM above your normal idle speed (from someone's tutorial on how to adjust idle speed).

 

Update:

Still got the bouncing idle this morning. Later today I ran out for an errand and when I turned the car back on after it had sat for about 15 minutes, I got the 3k idle again. Turned it off and back on and it was fine (although still idling higher than it should).

I'm starting to think I should grab a replacement TB from a junkyard or something....

 

Spec out your TPS by the Haynes method..

Also did you make sure the throttle cable/linkage isn't binding somewhere...

I don't think it's a TB issue... maybe an IACV or TPS or vaccum leak (I'm not ruling that out yet).

 

Here's what I was talking about:



The top end of that hose definitely leads to something on the back of the plenum. It made removing the plenum a bit of a pain...

 

I knew that was the hose you were referring to in your earlier post. Now that I looked at it again, I just realized what it is. It's a coolant hose. So it is NOT vacuum related as I originally suggested. If you trace the hose and connection lines indicated on the picture you posted, you'll see that the hose basically traces all the way back to the metal coolant log (where the ECTS, etc. plug in).

So this is not likely to be the cause of your high idle.

 

Have you tried to adjust the idle using the idle adjustment on the TB?

 

After a cold start, how does the IAC assembly determine when the temp has increased to the point that it no longer needs the fast idle? Does it have its own temp sensing method or does it get a signal from the ECU?

 

Note: all this is just my best guess - I'm not initimately familiar with this area:

Thats part of the coolant bypass through the throttle body. I know there is definitely an expansion valve (or something like it) that allows more air into the plenum while the car is cold. As the coolant warms up, the air flow is reduced by the expanding valve. I'm not sure of what role the FIC plays. The ECU definitely triggers them - they are solenoids IIRC (two of them, the FIC and there is one more).

Sorry to be so vague..

 

Okay. So, the coolant is part of what determines whether to use fast idle? If that's the case, could it be that the little bend in the new hose I put in is causing the problem by restricting coolant flow?

 

I suppose it's possible... The way the coolant lines work is that there is an inlet and outlet on the throttle body itself. (I can't remember which is which). One coolant port from the TB connects to the upper IM coolant port (right under the EGR port). The C-shaped hose you are talking about connects to the other side of the coolant pass-through on the plenum and back into the metal coolant lines that eventually go back to the main coolant log. So you could have a situation where the coolant is not flowing through the entire bypass (TB/plenum) and therefore not allowing the car to settle into it's normal warm idle-speed.

All I can say is that it's going to be a b*itch to replace that small hose - since you'll have to pull the plenum to get to it.

Can you get your fingers back there.. I know if I remove the IACV, I can see the hose fairly clearly - perhaps you can remove the IACV and see if the hose is kinked badly enough to restrict flow... if it is, order the replacement nissan part and swap it out. You could also warm up the car and see if you feel the hoses into/out of the TB get warm(er)... i.e if the fluid is indeed not flowing through as it should, than you may notice that those hoses aren't getting hot like they should...

If you need a "sense" of how hot they should get, let me know, I'll check when I get home tonight (i.e. after a long drive).

 

Thanks again. Let me see if I can get at it and if it's actually restricting flow. If it is, I'll try to replace it with some more flexible tubing that I found at Autozone and see what happens.

 

UPDATE:

Well, as best as I can tell, it's not a coolant flow issue. It also can't be a gasket problem because it's been recurring at high temps sometimes as well.

I have noticed that even on the occasion that it starts and idles fairly normally, the instant I start moving and then put the clutch in, the idle wants to jump back up to 2000 or more. Sometimes if I come to a stop it takes a LONG time to come back down to normal idle speed... and sometimes it just pins itself at 3000 and doesn't want to come back down no matter what I do.

Now, some weird things that lead me to believe this is might be electrical- or fuel-related:

1. I played with the fast idle cam adjustment screw and got the same results. It's as though something is telling the engine that it needs 3000 rpm, and it actually moves the fast idle cam until it gets that.

2. If I run the car for a short trip, turn it off for a few minutes, and then get back in and turn it on, it almost always jumps up to 3000 rpm.

3. Killing and restarting the engine at least once sometimes fixes the problem, at least temporarily.


If anyone has any further insights, PLEASE let me know...

 

doodfood, have you resolved this yet?

i'm having a surging idle issue as well...... partly because of my stupidity. i partly installed an 00vi setup, had problems, and then went back to stock. now my idle is surging.

i am getting a hissing/high pitched whistling noise, so could that be a vacuum leak? i'll try spraying tb cleaner around the gaskets tomorrow.

 

I don't think I did. I just turned the screw for the fast idle cam all the way out so that the FIC wouldn't do anything. The problem never came back.

Your case definitely sounds like a vaccuum leak, though.

 

which direction do you turn the fast idle cam and what's the consequence when you turn it in that direction? i may need to adjust mine.

so i did resolve my problem today, i think the high pitched whistle was coming from around where the lower IM meets the head. i had to take everything out and put it back in again very carefully and made sure to torque down all bolts to spec. but my car sounds fine now. thanks.

 

my brother's 93 Honda Prelude did something very similar to this. we fought with it for over a month, checking everything from the TPS to plugs, etc. we came up with the idea to go get a new throttle body and see what happens.....believe it or not, we put the new TB on and it resolved it and have had no problems since. not saying this is the case with your car, as all cars are different, but i wouldn't rule it out completely if i were you. chedk your local junkyards and see what you might pick one up for.


good luck man