Weird rpm movement

Hey guys, just did a bit of work to my 4.0 tacoma today. Spark plugs and oil change. Now when I press the clutch, I noticed a very large climb in rpm (several hundred rpm), the first time it happened I thought I just lifted the gas too late to shift, but I conducted an experiment to be sure. I started cruising at about 50 mph, put it in neutral and just started coasting with my feet completely off the pedals. I then watched my rpms climb to 2100 and drop to 1200, then climb to 2100, then drop to 1200, and climb again over and over and over, all the way to stop (still in neutral). When I get to a stop, it hovers perfectly without wavering at about 1100 (a touch high for idle). I'll also add that the engine was at operating temp. What the heck could do this?

 

Do we think a MAF sensor could be dirty/bad?

 

The MAF would be a good starting point. Clean it and the throttle body.

 

That's entirely possible.

Did you disconnect the battery to reset the ECU after changing the plugs?

The engine my be trying to maintain a spark/timing map it used to use with either different resistance or gapped plugs.

If so it's going to take a LONG time to relearn until you do.

 

That’s actually a really interesting point. I hadn’t thought of it.

Just by chance I did actually decide to disconnect and clean up the connections on the battery posts and wire leads. So, inadvertently, I did do that!

Today, the climb and drop isn’t as bad, but even if I’m coasting in gear and then press the clutch and coast then (never touching the gas) my rpms still climb considerably.

 

I thought all manual transmission Tacoma's did that.

 

Check that you didn't knock off a vacuum line

 

Simple repair..

Don’t drive like that....

You have 4 things against you.
1
You worked on the truck.
2
You disconnected the battery
3
Your driving a std
4
Uncle Sam....


New parts
Cleared learned memory
Your driving like your not suppose to
EPA regs have to be met.
They keep the throttle open on decelerations on purpose for HC control.
It should relearn
It should calm down
But, will always do it.....

double check what you did.
Listen to the engine and see if it sounds differently.
It should be back to a normal idle now.
If it’s higher check for hoses not routed correctly.

 

I must be lucky.
I've never had an issue disconnecting the battery on my 2015 Tacoma 1GR-FE or my 2014 4R 1GR-FE. Both engines stumble upon 1st startup after reconnecting the battery. I simply restart and all is good. No learning needed. Tacoma/4R run as they did before disconnecting the battery.

 

Try cleaning the carbon off of the throttle plate and sometimes letting it idle a couple minutes and a quick road test, it may just be all it needs to be back to normal. I use a rag and carb cleaner sprayed on the rag and wipe it out the best I can. You could spray the cleaner into the throtttle body and wipe it out. To much will make a hard long start sometimes. But it’ll start with some pedal action

 

Thanks all! I drove it around this morning as I ran errands and it got better as the day went on. The vacuum suggestion was also a good one. After I finished putting the spark plugs in, I ran it and heard one of them was still disconnected. Got that squared away before I even moved it. I think the winner here was the disconnecting the battery and allowing the computer to relearn. Generally, I'd imagine just about all spark plugs for any given model should be about identical, but perhaps there is less resistance cause these are newer and never used. I don't know for sure, all I know is that it got better and I didn't change anything since I posted last night.

 

Check all the vacuum lines for dry rot