1999 Altima, need help w revving too fast cold and harsh accel/decel

[merc68k]

Hi guys,

I posted once before about my 1999 Altima. It's got a strange problem, or problems.. they may or may not be related.

When I start it cold, wants to rev up towards 2500 rpm. Until it warms up, every time I come to a stop and put the clutch pedal in, it whips up to 2000rpm or so and hangs there for a few seconds before coming back down to a fast idle.

This continues to happen until the car has warmed up, AND I come to a stop and let it come back down to idle speed for a few seconds. Once I do this, it usually doesn't rev up again at idle. If I never get a chance to stop and idle, even if it's an hour long drive, for example, it will rev up as soon as I come to a stop, even though the engine is warmed up at that point.

The other thing is, there is an abrupt lurch when I ease into or out of the gas when cruising between 1500 and 2000 rpm. It doesn't matter how slowly I try to feather the gas, it's always an abrupt jolt. This gets better once the idle has settled down (above), but it's still apparent even then.

I have noticed that when I am stopped in neutral, and ease into the gas pedal, once the revs get past 1250 rpm they suddenly jump up to 2000+... and if I at that point start easing off the gas, they will immediately drop back to 1250 or so. I am assuming this is what is causing the harshness when I am cruising and trying to ease in and out of the throttle.

I posted about this problem a few months ago, and Nistech suggested I should try adjusting my TPS.. I actually was able to finally free the screws up this past weekend, and tried adjusting the TPS fully clockwise and counterclockwise, but neither helped -- one adjustment made the problem worse until I reset the idle position memory, and then it was back to normal.

There's a third symptom too, and that's a slight hesitation off idle when I blip the gas. This is most obvious when I've just restarted the car and it's still warm, say after I've parked and gone into a store for 5 minutes. There's a noticeable miss, you can see the tach dip slightly, and then it responds.

I'm at a loss, now more than ever, as to what the problem might be.. I've been battling with it for a long time now, and had it to the dealer a few times, but they think it's acting normally, which I don't buy.

I've ruled out:

*Plugs, wires, dist cap & rotor (new)*O2 sensor (front, new)*Coolant temp sensor (new)*Air filter (not dirty)*Leak in the intake manifold/rubber hose -- I plugged the end of the intake hose with a plastic bag, then blew into the PCV breather, and there was almost no leakage.. certainly not enough to come into play with a freely breathing intake.*TPS -- adjusted it both ways and saw no improvement*EGR valve -- it's clean, and disconnecting it makes no difference*IAT sensor -- tests ok*MAF sensor -- test ok according to service manual, and on a scanner it shows the expected response to throttle opening*Fuel pressure regulator - tested OK*Fuel filter - new*Idle speed valve - new (replaced due to seized idle screw)*Timing -- set 20deg. btdc at idle

I still suspect something like:

*Vacuum leak somewhere I haven't been able to find*PCV valve stuck open (dealer thought this was a remote possibility and I've read a few posts where a bad PCV valve caused weird idle issues)*Bad motor/trans mounts -- maybe there is enough slop in the system to make the abruptness in the throttle worse than it would be otherwise? That still leaves the hesitation / revving as an issue...

Any suggestions what else I might look at?? The car runs fine otherwise and would feel so much better if I could find what's up here... and it seems like I'm not going to get any help from the dealer...

Thanks in advance!!

[Eikon]

Have you tried removing and cleaning your IACV (Idle Air Control Valve) and AAC (Auxiliary Air Controller)? Those two control air into the manifold seperately from the throttle body. Perhaps the spring is sticking or the solonoid is bad? Try using some soap and water and carb cleaner on the mechanical parts... clean out any grease and grime..

Second suggestion.. Are you sure the throttle body is operating properly.. perhaps the springs that control the butterfly are not working so well.. Maybe they jump open rather than ease open?

Do you feel any movement in the throttle cable when it does this?

Have you tried starting the car with the hood open.. then blipping the throttle with your hand on the throttle body? Watch with your eyes and see if you can find anything.?

[merc68k]

Have you tried removing and cleaning your IACV (Idle Air Control Valve) and AAC (Auxiliary Air Controller)? Those two control air into the manifold seperately from the throttle body. Perhaps the spring is sticking or the solonoid is bad? Try using some soap and water and carb cleaner on the mechanical parts... clean out any grease and grime..

Those two were actually replaced when I had the idle screw assembly replaced.. so they wouldn't be gummed up at all.. and there was no change after they were put in.

Quote »Second suggestion.. Are you sure the throttle body is operating properly.. perhaps the springs that control the butterfly are not working so well.. Maybe they jump open rather than ease open? Do you feel any movement in the throttle cable when it does this?[/quote]No, it operates smoothly and there is no jerking at all -- the butterfly doesn't slop around on its shaft at all, and there doesn't seem to be any play between it and where the arm attached to the cable connects.

Quote »Have you tried starting the car with the hood open.. then blipping the throttle with your hand on the throttle body? Watch with your eyes and see if you can find anything.?[/quote]I have, but I haven't had any finding anything. About the only thing I might expect to see/hear would be the sound of air getting in somewhere other than at the intake, but I don't get anything like that. I've tried wiggling all the connectors I can find and tapping lightly on the MAF sensor, injectors, etc, all without any change in the engine too.

Thanks for the suggestions though!

[Eikon]

Boy, tough one you got there..

You obviously know your way around an engine...better than I do by the sounds of it... so I'm just going to toss out a couple random ideas... maybe one will slick with you..

-I'm sure the dealer pulled codes from the ECU.?? Did they tell you what was tripped... Perhaps you can stop by a car parts store (autozone for example) and have them run codes to double check.

-Perhaps your ECU is dodgy... I wonder if you could "borrow" a replacement from someone to see if it acts any differently?

-

[merc68k]

Boy, tough one you got there.. You obviously know your way around an engine...better than I do by the sounds of it... so I'm just going to toss out a couple random ideas... maybe one will slick with you..

Well, I'm certainly no expert.. I've just picked up what I know by tinkering and reading online, as well as from the odd mistake I'd like to think I've covered almost everything that could be causing my issue though.

Quote »-I'm sure the dealer pulled codes from the ECU.?? Did they tell you what was tripped... Perhaps you can stop by a car parts store (autozone for example) and have them run codes to double check. [/quote]Well, I have checked them myself and there are never any stored... As far as the ECU is concerned everything is cool...

Quote »-Perhaps your ECU is dodgy... I wonder if you could "borrow" a replacement from someone to see if it acts any differently?[/quote]That's a possibility I've considered too.. but it works fine otherwise so it seems unlikely that'd be the problem. Of course once everything else is eliminated, the unlikely causes start to be a little more likely!

Along the same lines as a bad ECU, I've checked the grounds around the engine compartment, and cleaned & reattached them, and the voltages seem fine at the battery, so I think the electricals are all in order... I don't know if there are any other checks I can do for, eg, bad grounds, although I did test between some of the grounds near the injectors and the neg. terminal on the battery, and noticed there's a few volts of difference between those 2 points, which seemed a little odd to me... Any thoughts on that?

Thanks for the suggestions, I figure sooner or later someone's gotta think of something that'll turn out to be the problem.

[Eikon]

Along the same lines as a bad ECU, I've checked the grounds around the engine compartment, and cleaned & reattached them, and the voltages seem fine at the battery, so I think the electricals are all in order... I don't know if there are any other checks I can do for, eg, bad grounds, although I did test between some of the grounds near the injectors and the neg. terminal on the battery, and noticed there's a few volts of difference between those 2 points, which seemed a little odd to me... Any thoughts on that?

Thanks for the suggestions, I figure sooner or later someone's gotta think of something that'll turn out to be the problem.

I've been in cars in the past that have a tendency to bog down or idle too low.. As they idle down too low.. the ecu freaks and bounces the idle up nice and high keep it from stalling out. What if you adjusted your idle speed up a little bit. I'm not an Altima guy.. but I would guess stock idle is somewhere between 700 and 800 rpm.. where do you idle? What if you bumped the idle speed up a bit?I wonder if your throttle position sensor is a little tweaked and when the car is cold it's oversensative and makes the ecu think the car is going to stall out.. Maybe that's why it's blipping up the rpms..???

again... just thinking out loud... hopefully something will click sooner or later...

Anybody else have any ideas??? Wes?

[merc68k]

Well, here's another piece of the story that I left out to try to keep the post relatively short... originally, it idled too high all the time. Around 1000, even when it was warmed up. It would rev up and hang around 2000 rpm almost every time I came to a stop.

I couldn't do anything about this due to my idle adjust screw being seized.

For a while, I had a rubber washer in the air hose that runs to the IACV valve, which was limiting the air that went to the IACV, and that worked -- the idle was close to normal and the over-revving was gone. But the revs dropped a lot between shifts, and in the summer, the engine would bog down when the A/C came on.

I finally had the IACV assembly replaced, and I was able to get the idle down to where it's supposed to be (750), it's actually maybe a touch too low... but the problem existed before the idle was this low anyway.

I think the same as you -- that maybe the ECU is seeing something and trying to compensate for it.. maybe related to that miss that I see when I blip the throttle. I know that it is opening the IACV as I ease open the throttle, and when I unplug the IACV, the overrevving goes away, and the harsh accel/decel is gone too. I've been wondering if at a certain point (rpms) there's a change in the intake stream that throws things off... maybe the PCV valve, if it's sticky, opens or closes, and causes the ECU to try to compensate??

[merc68k]

...Bump?...