Brief RPM dive when stopped.

gbrettin

I'm having a minor issue on my car where my RPM dips down a little too much after I bring my car to a stop. For example, say I'm driving my car normal and come to a stop sign my engine drops RPM's a little too much and I notice that my charging system takes a dip to about 12v too (because the engine rpm drops). This only happens for about 2 sec and then picks back up to normal idle and then the charging system goes back to 14.5 like normal.

I'm concerned about these drops on the system because I don't want to strain the charging system. My car has z1 urethane mounts so my car shudders when the RPM drops off. I understand that the mounts are stiffer so the car will shudder at lower RPM. I don't believe that my car did it last year after I had the mounts installed but I'm not sure. Maybe I'm just focusing on it more because of the engine mounts?

I've had my car back on the road for about 3 weeks now. Previously my car has been sitting outside for the winter. My first tank of gas I added STP Complete Fuel System cleaner. My car does not dog out at any RPM and feels right other than the quick dip in RPM at a stop.

I was thinking about cleaning the throttle bodies on my car (which has 55k miles) but figured I would stop here and ask what others thought first.

Thanks

jcosta79

That's interesting. Has the car been tuned ever? Has the car's battery been disconnected recently? Only 2 things that come to mind.

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FPenvy

might be the ECU relearning stuff if it sat for awhile.

i know sometimes when i come to a stop and not in the right gear or brake hard in a high gear (like when dbags brake check me in traffic) i'll see a little dip in my RPMs but it jumps right back up for me. never noticed a charge system difference yet either.

i actually i'm a little worried that something in my tune changed over the winter from sitting so long.

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SouthArk370Z

At 55k miles, it would probably be a good idea to go ahead and clean the throttle bodies. It's not all that easy to remove the TBs but it's not all that difficult either. Check some of the DIYs on this site and see if you feel comfortable doing it. While you're in there, I'd go ahead and clean the MAFs (super-easy job; all you need is a big Phillips screwdriver and some MAF cleaner).

But that's just a shotgun "fix" - do some data monitoring/logging to help pinpoint the problem.

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gbrettin

Nope, the car has not been tuned. The battery was dead as a door nail so I had take the battery out and charge it for 24hrs on a slow charge. The car starts fine but I'll go test the battery.

gbrettin

You think it would take 3 weeks? I thought it would only take a couple days at most.

FPenvy

depends on the milage. if you're only putting 5-10 miles a day on it then yea it could take longer.

take a normal car when they clear a check engine light or whatever. it takes about 75-100 miles to fully fix itself.

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gbrettin

I'm going to be tearing into the car pretty soon. I'll hit the TB's and MAFs at the same time. I figured 55k on the ol' lady it's about time I clean them too but I wasn't sure if it was possible if the TB's (or MAF for that matter) could cause a dip in RPM.

I'll snag a video later so you guys can see what I'm talking about.

gbrettin

Eh, I already been through 3 tanks of gas.

FPenvy

well then lol should be reset or learned everything by now

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critical

throttle bodies.

that's it.

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jcosta79

My guess would be battery.

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DEpointfive0

My car does the same thing. Z1 mounts, but 20% UD pulley (so I don't look at the volts)

For me, it dips and comes back, back and forth. F-ing annoying... I have an auto as well, and it only does it in Drive. In park, I just feel mild vibrations

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gbrettin

Just found this:

"Nissan throttle bodies are notorious for getting dirty pretty quickly. If your car has issues with the RPM dropping at idle, it is probably a dirty TB."

DIY Clean your Throttle Bodies - MyG37

The issue sounds like it fits the bill.

gbrettin

Good to know. I have a 7AT too and will be putting NST Pulleys on... if they ever ship.