So every couple of weeks or so...I experience this weird issue with my car.

I have a 99 SE.

Normally, when you start the car after it's been sitting for a few hours, the RPM's are at 1.2k or so and gradually go down to 700 or so when the car is fully warmed up. However, lately, I have been experiencing that the car starts at 1.2k, goes to 700k, go back up to 1k, goes down to 700k, goes back up to 1.2k, etc. etc. etc.

I maintain the car religiously. The plugs were changed about 6,000 miles ago, air filter (Nissan paper filter) about 2,000 miles ago, PCV valve 500 miles ago, Oil is at about 4,000 miles (full amsoil synthetic). I have just under 65,000 miles on the car.

Also, when I am at a light in drive, it will do the same thing and unless I hold my foot down hard on the brake pedal, my car will creep forward in surges by itself. It's like a horse, I have to keep reigning her in.

What do you guys think?

I have no CEL, and the only ghost code I have is for running lean (I have SS AutoChrome headers, fed. spec y-pipe, magnaflow high-flow cat, budget b-pipe, OEM muffler...I'm not tuned in any way).

 

Sounds like a vaccum leak and your IACV is struggleing to keep your idle at a steady rate.

-matt

 

So I should be looking for it in the IACV area? But that leads to my next question...if it was a leak...wouldn't it be consistant until I fixed it? It started on Saturday and the last time this happened was maybe 5 weeks ago...

 

I agree, it sounds like a leak to me also, in fact Im almost certain it is. They can be tempramental, for example, they can occur at different temperatures. I had one only once my car warmed up, after about 15 minutes of driving. Its possible that when you replaced the PCV that maybe the hose is split, or not on all the way. The IACV is a possibility but with such low miles(dude, 65K! wow) I doubt it has gone bad.

 

If no visible cracks are visible...is there any other way to check for a leak? I've never had to do that before...

 

Propane torch. Turn the propane on but don't light the torch. Move it around your intake manifold, TB, IACV, and vacuum lines. If you hear your idle change right when you move the propane over a spot, you know thats where your leak is.

Then again, if your idle is fluctuating that might be hard to pinpoint.

 

What's the risk factor getting blown to mars? lol.

So the car should be running, and then I just move it around the general area where the leak probably is? How much will the idle change? Will it be as noticeable as unplugging a working coil pack?

 

Dont do that. Just get some carb cleaner and fully warm your engine up and just sray that around areas you think will be leaking. The idle will dip, and the engine might even die.

-matt

 

I'll go route 2...seems a bit safer lol. Thanks guys...

 

The propane trick is just as safe, and cleaner. It's not going to blow anything up. Just do it in a well ventilated area, like not in a garage, an make sure you arent around a camp fire. Any "explosions" will take place inside the engine where explosions are supposed to happen. Carb spray can take the finish off/corrode throttle linkage and other metal parts, etc. If you're going to do that, make sure you rinse the engine off afterwards. Suspect a vac leak, IACV, TPS, and MAF. A flakey/bad MAF will cause unstable idle, and probably a lean code/condition in any car, as will a vac leak. It's more fun using a multimeter to test the electrical stuff (assuming you know what #'s to look for) before tracking down a vac leak. Although, I've always had good times with propane... So, your call.
I would suspect the MAF mostly because if your car has such few miles but is up in age, that means it has sat more than others. That means any moisture that naturally gets inside things has a hard time getting burned off without consistantly running the engine and getting temps up. That was worded all wrong, but you get me... The element in most mafs is made up of alluminum or copper, several ply thick. The moisture gets inside and seperates the element into pieces. This is how VW technicians explain VW's older notorious MAF failures for lower mileage/old in age cars. I'm sure the same concept applies to other cars/other parts.

 

I think I have a spare MAF....I might just put that in and give it a whack.

 

Whack it hard.
And exhaust mods wouldn't cause a lean code/condition. If anything, because you are increasing flow, the rear 02 sensor(s), would trigger a false rich code.

 

I thought changing of the headers cause it to lean or get rich?

Who knows...I'm not really into performance. I got new piping cause my car is a NE car and the pipes were rusted to hell. I prefer show and no go...lol.

Thanks for the help guys.

 

Im still jealous you only have 65K on your car.

 

I got it in late 06 with 26,004kmi . lol...sorry to rub it in. But yeah, I'm going to be driving this car for MANY more years.

Anyway...work day is over...later folks. Thanks for the suggestions, I'll try them.

 

Haha. I am only at 97K on my 97 so Im not that jealous. Haha.

Also, if you think it may be a vacuum leak you can try this primitive method, but it works quite well.

Remove the intake accordion and use duct tape to seal the throttle body port. Then remove the brake booster line, and blow into the hose. You shouldn't be able to blow, but if you can, and you hear air escaping somewhere, it could be your leak. Try to track it down and find out where the air is coming from.

 

As for the propane torch vacuum leak method, no worries, if worse comes to worse and something ignites the torch...it does just that...lights the torch just as if you put a lighter up to it.

I wouldn't worry about it though, there isn't anything that would light the propane, and if there was, it would light off the carb cleaner as you spray it anyway.

 

I finally had the chance to do the work.

It was a dirty MAF. As it was last time this happened. Why the hell is my MAF getting so dirty? I had a K&N filter the first time, which came over oiled out of the box...but I've been using a Nissan OEM from the dealer the last two filter changes and it's still getting dirty. On my 97, I never had this problem.

I cleaned it with CRC MAF Sensor cleaner and it's been good for a week now.

 

Not sure. Its possible that your MAF is on the way out. Mine died recently and CRC cleaner only made it worse. Then again, one spec of oil or dirt can affect the heat transfer on the hot wire so...who knows. Glad you found out though!