Needing some help with this and can’t figure it out.

Long story short: what could cause engine to rev up to almost 2K rpm whenever I start on a warm engine except when first started cold? It immediately drops back down, but I know that’s not how it’s supposed to be.

Also: had a most unexpected issue the other day: went to crank after sitting for a week (albeit it was left on less than 1/4 tank). It would crank and crank and not turn over. Checked fuel pump fuse and all was good. Tightened negative battery cable (was a bit loose). Everything seemed right but it just wouldn’t catch. Finally I unplugged MAF sensor (recently replaced from eBay) and it started up after a couple of times. Plugged MAF back in, and died immediately. But then started back up fine with maf plugged.

I don’t want to blame MAF right off bat, since it did cure my constant stalling issue a couple months ago. But I don’t know. I’ve changed fuel pressure regulator twice, intake manifold gasket is new (may need to double check the bolts).

I’m just stumped! only codes I’m getting is an ignition coil wire and EGR circuit and the occasional torque converter solenoid malfunction. It’s disappointing because I can’t find a mechanic who really wants to spend the time to get it right. It’s running great and strong, but idk which component is causing it to start like crap. Most times it starts up quick, but it’ll rev up.

Also noticed again today when out to start after sitting all night and morning, it struggled a couple of times. It’ll crank and the engine will almost “detonate” in vibration. Changing knock sensor didn’t help.

I am glad to say though, my gas mileage has improved dramatically. And I have quite a bit of power on the wheels.

 

The IACV or Intake Air Control Valve might need to be cleaned.

I took mine apart and removed the deposits with
carburetor spray.

You should also clean your throttle body plate.
Buy some CRC Throttle Body Spray.
There are instructions on you tube.
I scrub with an old tooth brush and clean up with a paper towel.

seems like you need to clean out your egr system.
The egr system and the door handle tube.
this repair has been discussed on this forum many times. A Google search will find it.

 

I think ones’s first steps should always be to address issues that are creating DTCs ...

If your your car is telling you something’s wrong, fix it. Then move on to the things it’s not telling you.

 

I actually replaced the IACV back when the stalling issue from the MAF had me thinking it was that. Same as throttle body cleaning I’m quite aware of (when I first brought it back in 2012, it would start but immediately stall on cold start unless I pressed the gas). A mechanic buddy was able to refer me to do a throttle body cleaning.

I’ll look into intake air control valve and the sensor. As for the EGR thing, I’ve read the write up for it before. I’ve also replaced the EGR valve itself but not the tube (this was few years ago when trying to pass inspection). I have had success on clearing the EGR code on my 98 Q45 by just flooding the EGR opening with sea foam deep creep. It was just as bad as the Maxima was. So idk why it still comes up.

But this is all leading me to some ideas. I think the EGR gasket might of fell off back when I was doing the fuel injectors and had the plenum off a few months ago. I’m just trying to figure out when it started because for the longest time, the starting idle was perfect, just above 1,000 rpm in Park. And the idle has been adjusted to spec and is fine, it’s only at startup for a brief second, that it revs up close to 2,000. Coupled with a noisy compressor bearing, it really turns heads and more of like, what’s wrong his car kind of way lol.

One thing I did notice: it seems my trusty mechanics removed my charcoal canister and left it venting to the open. This was during a disagnostic where there was still charcoal in the line. But the valve and canister was replaced by me a couple years ago around the same time as the EGR valve. Whatever charcoal was left, was likely from the old one. Needless to say, I was pissed. I did put a replacement back on there, but it didn’t make a change in the initial startup rpm.

 

The egr to door handle gasket like to pivot upside down if you are not paying attention. That would create an air leak. Also the high idle issue.

the missing charcoal canister could also create an air leak when the solenoid opens back there.

Id remove the connector to the charcoal canister until you you replace the canister.

Also replace the gasket between the door handle tube and the ear.

I also advise cleaning out the door handle tube. It has an additional gasket on the other side.

 

Update: no luck.

Also want as far as changing out the TPS sensor. After just removing and replacing the old one to clean it (it was spotless and not open to the gunk of the throttle body), engine was acting strange, revving while driving, without input. Put in new one, adjusted the voltage to match proper idle. No more weird revs while driving but the starting idle still jumps up before coming down to normal. I didn’t realize TPSs were so finicky. The noise of the engine is exasperated by my compressor bearing. It literally sounds like I’m starting up a toy go-cart or something lol.

only codes I’m getting is same old egrc solenoid and something with the ignition. I wish someone woulda helped me figure this out when I spent $140 twice to have a shop and the dealer run a diagnostic on it. Think I might take it back to Nissan and argue with them lol.

 

An engine which revs by its self often has a vacuum leak somwhere. It's often at the egr door handle tube because the gasket likes to rotate and call out of place as its being installed.

 

Update:

So going based on codes: I was able to clear a EGRC solenoid code by buying that part. Since then I’ve also brought a new TPS (throttle position sensor). I’m just hoping I have this thing right:

I don’t have a voltage meter but I was able to take the idle down as low as it’ll go between that and adjusting the IACV. Still can’t get lower than about 925 rpm on neutral. I read that you shouldn’t be able to open the throttle body when rotating it, so I pulled the air intake just to make sure. But it’s fine. Had to tweak it a couple of times because each time I did anything to it, it would make the idle up to about 2,000.

It’s driving fine, everything fine…except at startup it’ll bump up to 1,700 for a quick second, and then drop back down to 900-1,000.

what bugs me is I can’t remember how long this has been going on. I only noticed it because my Q45 idles so smoothly: got it down to 650 rpm in neutral. But can’t for whatever reason get the Maxima lower than 900.

I did check and reinstall the EGR gasket that attaches to plenum, even glued it with sealant. No difference. Manifold plenum gasket is new and was replaced earlier this year. Only code I have left now is: Ignition signal P1320.