RPM's bouncing between 2000 rpm to 1500 rpm

[Im Lon 2]

Hi all,

I have a 2001 Chevy Impala 3.8 with 191,000

Over the past couple of weeks I have been working on my car, because of the EGR valve Code came on (P1404 & P0404). Changed out the EGR Valve and code came back after clearing the codes.

Then I went back and took the EGR valve back off along with the throttle body, and cleaned everything with carb cleaner. Cleaned the MAF sensor with MAF Sensor Cleaner. Took off the MAP sensor to check the PCV valve, and the MAP sensor had snapped into two piece, so I replaced that sensor as well. Changed the air filter, and changed the oil, and put in Sea Foam in the gas tank when I filled up.

Got the code to go away on Saturday and now I have an issue with the RPM’s Bouncing when doing around 35-45 mph RPMS bounce back in forth between 2000 and 1500. Feel’s like a wave on a boat. This happens not during acceleration, but when easing up on the gas to maintain the speed. I have noticed this only in the 35-45 MPH range, so Far any how.

It’s not thronging any codes at this time, so not really sure where to start.

Any help would be appreciated.

[Moppie]

Have you checked for a Vacuum leak?
That will often cause surging, but usually at idle.

[Im Lon 2]

I just read that after posting this tread where it shows multiple matching thread below. I had took off the hose on the brake booster Saturday and had added Seafoam in there as well.. Forgot to post that.. I might have not got it back on there snug. I will test that first..

[Moppie]

Originally Posted by Im Lon 2

I just read that after posting this tread where it shows multiple matching thread below.

Yip, the forum runs a little search on your thread title and shows matching threads, or similar threads below.
Can be very useful


Also check any connections around the manifold.
You may have knocked something while working on the MAF etc.

[Im Lon 2]

I have checked the brake booster that is on nice and snug.

When reading one of the other forums I noticed someone stating theirs doing it only in OD, so on the way home 45 min drive I dropped mine down into 3rd (till the HWY) and was not able to duplicate the surge. Now I have to go back and find the thread I was reading on that to see what the issue may be. I will also continue driving it in 3rd for the next couple of days to make sure it does not do it while in 3rd.

I will check the connections again on the throttle body to make sure everything is connected correctly.

[Im Lon 2]

I thinking (not 100% sure) but there maybe a chance that the trottle body is not tight I can see the red gasket on the front side. If i disconnect the throttle body away do I have to replace the throttle body gasket that I just replaced, if it look ok?

[Moppie]

Originally Posted by Im Lon 2

I thinking (not 100% sure) but there maybe a chance that the trottle body is not tight I can see the red gasket on the front side. If i disconnect the throttle body away do I have to replace the throttle body gasket that I just replaced, if it look ok?

Shouldn't have too, unless you used lots of sealant, or the gasket is damaged.

[Im Lon 2]

Ok car does do this in 3rd gear.

Originally Posted by Moppie

Shouldn't have too, unless you used lots of sealant, or the gasket is damaged.

I did use sealant. I have replace this seal 3 times and never used any type of sealant in the past. Should I? FYI I have the rubber seal.

I plan on working on it some time Next week once it cools down a little.

[Moppie]

Originally Posted by Im Lon 2

Ok car does do this in 3rd gear.


I did use sealant. I have replace this seal 3 times and never used any type of sealant in the past. Should I? FYI I have the rubber seal.

I plan on working on it some time Next week once it cools down a little.

To be honest, I know. We don't get a lot of Impalas here

However, from my experience you don't need sealant on intake gaskets, and you don't use it on rubber gaskets either.
But, that could be very different for your car, as there maybe coolant lines etc, running through it.

[Im Lon 2]

Ok finally got some time to get back to working on the car. We looked every where for a vacuum leak and could not find any cracks anywhere. we even sprayed carb cleaner around the lines to see if the car would react in any way... Nothing.

Took off the throttle body, and made sure it was nice and sung. Auto place told me to try the TPS (Throttle Position Sensor) so I replaced that and still the same thing. Do you have to disconnect the Battery for it to read the new TPS?

While I was taking off the sensors I checked the Idle Control Sensor and it looks awful. The auto store is closed now so we cleaned it up, still look pretty rough. Not sure if that would be the issue or not, since it idles fine, and only does this around 1500 rpms

I wish the car would show a light so I can figure this out. Last time it didn't through a code it ended up being the CAT. That was in 07 and 60,000 miles ago. Could that be an idea?

[Im Lon 2]

I finally got the engine light to flash the other morning. So I replaced plugs and wires this weekend. 200 miles later car runs so much better and is not jumping around or doing the fishbite and more, but I'm still getting a misfire in cylinder 6 (only noticed this sitting at a redlight). I will replace the coil packs this weekend. I'm hoping this will take care of all my issues.

Thanks everyone for your help.