Hey guys,

So this weekend, I just completed replacing my valve cover gaskets, along with any other gaskets along the way. I was able to do all of this without a check engine light coming on after. However, my car is now running rough at idle. Less so when I'm driving, but I can still feel it. I sprayed down the engine bay with brake clean while it was running, in any spots that might have a vacuum leak. However, it didn't choke it out. This leads me to believe this is not a vacuum leak. Anyone have suggestions as to what my issue could be?

 

One area to check is the EGR tube gasket. Sometimes when reinstalling the gasket gets out of position and creates a leak. Double check that the gasket is in place

 

Yes, that's correct. It likes to pivot.

You do have a vacuum leak. It could be at that gasket, or another one.

 

Thanks guys, I might just pay to have my work do a smoke test to see where any vacuum leaks could be

 

I did a whole intake refresh starting a little over a year ago. I couldn't find my air/vacuum leak. I made a smoke blower using a cheap soldering Iron from Harbor Freight, a mason jar, cotton towel with mineral oil, the cheapest aquarium air pump on amazon. Clear plastic hoses and brass threaded hose connectors for the jar lid. Pumped smoke in through many places and finally one revealed the UIM gasket bulging out UNDER the manifold where I couldn't see. That's what I get doing it at night in a NY Winter.

This is the thread where I went through everything: https://maxima.org/forums/4th-genera...dle-grief.html

Hope this helps!

 

Yeah, I did all of my work in 20-30 degree weather after I'd get off work at 6 every day, so I can relate That's what I get for only having one functioning vehicle. Probably just gonna invest in a smoke machine eventually, but for now I'm gonna leave it for my work to find

 

Alright, so update: My work took a look and didn’t even smoke test 🤦🏻‍♂️ BUT they did find a corroded wire going into my TPS, and there is corrosion on the bottom left section of my TB. Anyone know what I’m talking about? I can’t seem to find out what it is, but there’s all sorts of blue corrosion caking it.

 

Perhaps you can replace the bad wiring to the TPS by chopping off the corresponding wiring from a maxima at the junk yard. Or buy a new pigtail.

The throttle body has heated coolant flowing through it.
It's there to prevent icing in the throttle body.
The passages can corrode and start to leak.

You could find another throttle body at the wrecking yard. Or perhaps a member has one they could sell you.
You might as well buy some CRC Throttle Body Cleaner.
Clean the interior of the TB with the cleaner, an old toothbrush and paper towels. Pay particular attention to the edges of the throttle plate. Idle might improve after this is done.

The heated throttle body prevents icing if the car is operated in moist air which is just above freezing.
ice could form in the air passage. The ice could cause stalling.

You want a heated tb if your climate is like that.
If you live in a region in which there is no moist air at temperatures below 40 F, you probably don't need that.
So it's possible to bypass the tb with a length of rubber hose which would replace the two connecting to the tb.

 

Yeah I have two 4th gens, one of which is currently my parts car until further notice. I’ve been thinking of pulling the connector off that one. Do you think the corroded wire could fix issues like bucking while accelerating, and stalling? I can’t seem to figure out the cause. With my TB, I’ve already done a full clean up job, as well as everything else down to the lower intake manifold

 

The bad wire not attached to to tps means that tge computer does not know tgat you have stepped on tge gas. So it does not send a signal to increase flow to the injectors. That's like having a vast accelerator pump on a carb. It will want to stall when you try to accelerate from idle.

all sensors ate there for a specific purpose. So of course their wiring needs to be intact.

So yes, use the wiring pigtail from the other car.

Your car engine should run much better.
The engine will run pretty much like new once everything it needs is done.

 

Awesome, thanks for the info! I’ll give it a shot

 

Just finished the wire repair last night, and my car is running ten times better! Now, the only issue I have left is the idling/stalling issue. When I go into neutral, whether it be by pushing in my clutch or shifting into neutral, my RPMs tend to go down to 500, then up to 800-900. However, sometimes it will try and stall on me. Luckily, since I drive a manual, I can kick the car back on with my clutch. I have a feeling this is my IACV, but I pulled the actuator out of its housing, and it seems to be moving properly. Any ideas? My car runs perfectly when in gear.

 

I stand corrected, she's still bucking I guess that shows how intermittent the issue is..

 

What you see underneath the throttle body that appears caked and green is the High Idle plunger. Think of it as a thermostat somewhat. The cars idle is raised slightly during a cold start and as it heats up, the plunger arm pulls back to lower the idle Once up to temp. This part is Mechanical in nature, however the PCM takes account for TPS value, CTS input and MAF inputs during a cold start . The high idle plunger typically fails causing a higher idle in most cases. It wont have any effect on the stalling.

The Low idle and bucking may be two separate things here. Did you remove or unscrew the TPS in any way.? How's the MAF intake tube and Box Look if its OEM..? When you dissembled the IAC Did you adjust it in anyway.? Several things come to mind, we'll need more Information.

 

The TPS on the throttle body currently installed is still in the factory position. I had installed a new one originally, but since I still had issues, I took the TB off my other Maxima with its TPS attached and installed it, in order to factor out the possibility of an error on my end. The MAF intake tube and box is all OEM, and nothing seems to be wrong there. The MAF sensor itself is new and aftermarket, however this issue was happening before I replaced it. I did adjust the IACV screw in an attempt to lower RPMs, but again, I did this after this issue was already occurring. In fact, the whole reason I pulled everything apart down to the valve covers was because of this. It was a “well I’m already here” kind of situation. I had made zero adjustments to anything when this issue became relevant.

 

Not sure if you unclogged the EGR tube, but if not, get that done. And if done... I'm thinking "Vacuum Leak" somewhere along all those places it can occur when you go that deep on the Intake.

Back to the smoke test. Unfortunately using a propane torch unlit to see if the idle raises as you put the propane where leaks can happen is hit or miss. But still an easy thing to try.

Nothing like 4th Gen Frustration! LOL

 

Yes, I cleaned out the EGR guide tube when I cleaned everything else. I’ll try the propane torch trick as soon as I can, and I’m also gonna pull a functional IACV off my other Maxima and throw it onto this one to see if that could be the issue.