RPM dip at stop

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FatherTime
Posts: 60
Joined: Sun Dec 22, 2019 8:24 pm

RPM dip at stop

Post by FatherTime »

Occasionally, with the engine warmed to normal operating temp, after coming to a stop, I get a quick dip in RPM's to about 500. The engine shakes a bit, then quickly recovers to normal idle (800 RPM). One thing I did notice, if I'm idling, and turn the blower fan directly to high, it does exactly the same thing. Maybe that's normal? IDK. As part of my 110k maintenance project I've already cleaned the throttle body and MAF sensor. It has a new battery that tested good. I still plan to install plugs, and clean the IAC valve. Any thoughts on this?

Also, what's recommended for plugs for this engine? (2009 base 1.8).
2009 Pontiac Vibe 1.8 FWD Manual Trans
Caretaker

Re: RPM dip at stop

Post by Caretaker »

Everything you stated is correct. I've been living with it for years. The trouble runs throughout the Corolla family lineup. My ace mechanic in San Diego went through everything, cleaning everything..............in the end, the issue remains. I've read that the throttle body has been re-engineered. Unless you have actual stalling, I'd leave well enough alone. You've obviously cleaned out the carbon and while the studdering is annoying, it hasn't resulted in any stalls for me. I do notice different performance from different gas blends. My Corolla Vibe seems to enjoy Sunoco and Shell gas better than Costco and Sam's Club gas. Look to the future: Subaru is putting the 2.5 liter engine in the Crosstrek this fall.
FatherTime
Posts: 60
Joined: Sun Dec 22, 2019 8:24 pm

Re: RPM dip at stop

Post by FatherTime »

Caretaker wrote: Thu Apr 16, 2020 3:10 pm Everything you stated is correct. I've been living with it for years. The trouble runs throughout the Corolla family lineup. My ace mechanic in San Diego went through everything, cleaning everything..............in the end, the issue remains. I've read that the throttle body has been re-engineered. Unless you have actual stalling, I'd leave well enough alone. You've obviously cleaned out the carbon and while the studdering is annoying, it hasn't resulted in any stalls for me. I do notice different performance from different gas blends. My Corolla Vibe seems to enjoy Sunoco and Shell gas better than Costco and Sam's Club gas. Look to the future: Subaru is putting the 2.5 liter engine in the Crosstrek this fall.
Thanks for the feedback. I have to say I'm a bit surprised that nobody else has chimed in on this :?:
2009 Pontiac Vibe 1.8 FWD Manual Trans
SSizler
Posts: 144
Joined: Tue Jan 21, 2020 7:06 pm
Location: Urbandale, Iowa

Re: RPM dip at stop

Post by SSizler »

Mine does the same thing, but seemed to get better / less noticable after replcing the PCV valve.
My PCV valve was completely stuck - no rattle or flow at all.
You can try replacing yours, it is a reasonably low cost item.
Just be sure to take your old one to the parts store with you.
There is more than 1 listed in the books, and my NAPA guy had to look thru 3 to find the correct thread size.
2003 Vibe Base / Frosty Mono / Moon & Tunes / Auto / 206k mi / Total Loss 1-23
2006 Vibe AWD / Lava Mono / Loaded w/Leather and Sport Pkg / 150k mi
Many other 2 & 4 wheel toys :mrgreen:
40 years with a wonderful woman / 2 adult kids
cptnsolo77
Posts: 1645
Joined: Sun Jul 29, 2007 4:05 am

Re: RPM dip at stop

Post by cptnsolo77 »

Had the same issue years ago. Changed the intake gasket, cleaned MAF sensor,PVC valve and throttle body. Still had the issue. Cleaned the IAC and it hasnt returned since.

This the link I used: viewtopic.php?f=17&t=36489&p=476353&hilit=iac#p476353
* 2003 Vibe Auto Satellite Silver w / Moons & Tunes
* Kenwood Excelon KDC-X597
* Polk DB651-Speakers
* Soundproofcow Roadblock R sound deadening in all doors
* Drop In K & N Filter
* NGK Iridium IX Plugs
* 27 MPG City/Highway with AC on
Zimm
Posts: 332
Joined: Wed Feb 03, 2010 1:47 pm

Re: RPM dip at stop

Post by Zimm »

my '10 base has had this since day 1. imo it's bad transmission programming. other things can help/hurt it, but the root cause is bad programming.
'10 Black w/1.8L AutoAir/PW/PL/PM
jolt
Posts: 945
Joined: Sun Mar 02, 2014 2:07 am
Location: Twin Cities, Minnesota

Re: RPM dip at stop

Post by jolt »

The 2009 vibe do not have a IAC, as they are drive by wire. The idle speed is controlled by the ECM and throttle body. If components in the throttle body are worn, it can make it very hard for the ECM to control the idle speed of the engine.

If you have any uncontrolled vacuum leaks it can be impossible for the ECM to control the idle speed. Check all vacuum hose connections and the hoses them self's. Check the evap system, check the power brake booster, ect..... anything that has vacuum on the car. About the PCV valve; just because it rattles does NOT mean the valve is good. Cut a old valve apart and look close at the tapered face of the valve. You will see small grooves cut in the face. These grooves meter the amount of air that pulled from the crankcase into the intake manifold by vacuum. These small grooves gets caked up and closed over time. The only way to clean them is to replace the valve so that the proper amount of air is being feed to the intake manifold in a regulated fashion.

When you cleaned the throttle body, you took it off the engine. Did you pull the side cover off and check the play in the plastic gears, the shafts for the gears, the butterfly shaft, because there needs to be no play in any of these parts or you are going to have dead spots or delays in how the ECM controls the idle speed. Also, did you measure the resistance on the signal pot to make sure the resistance values are linear through the whole range of travel of the pot. The pot wears, especially it the idle position because that is where it spends most of its time at, and will not give accurate information back to the ECM if its signal is not consistent.

All the parts in your car have wear on them and as things wear, they degrade. The only time you get a car to run like a new car, is to replace everything so that it is all new. A car is the sum of it's parts. Is it worth trying to fix this problem, that is a whole other matter as this problem can be a lot of little things that may cost more to fix then the car is worth.
FatherTime
Posts: 60
Joined: Sun Dec 22, 2019 8:24 pm

Re: RPM dip at stop

Post by FatherTime »

jolt wrote: Sun Apr 19, 2020 5:02 pm The 2009 vibe do not have a IAC, as they are drive by wire. The idle speed is controlled by the ECM and throttle body. If components in the throttle body are worn, it can make it very hard for the ECM to control the idle speed of the engine.

If you have any uncontrolled vacuum leaks it can be impossible for the ECM to control the idle speed. Check all vacuum hose connections and the hoses them self's. Check the evap system, check the power brake booster, ect..... anything that has vacuum on the car. About the PCV valve; just because it rattles does NOT mean the valve is good. Cut a old valve apart and look close at the tapered face of the valve. You will see small grooves cut in the face. These grooves meter the amount of air that pulled from the crankcase into the intake manifold by vacuum. These small grooves gets caked up and closed over time. The only way to clean them is to replace the valve so that the proper amount of air is being feed to the intake manifold in a regulated fashion.

When you cleaned the throttle body, you took it off the engine. Did you pull the side cover off and check the play in the plastic gears, the shafts for the gears, the butterfly shaft, because there needs to be no play in any of these parts or you are going to have dead spots or delays in how the ECM controls the idle speed. Also, did you measure the resistance on the signal pot to make sure the resistance values are linear through the whole range of travel of the pot. The pot wears, especially it the idle position because that is where it spends most of its time at, and will not give accurate information back to the ECM if its signal is not consistent.

All the parts in your car have wear on them and as things wear, they degrade. The only time you get a car to run like a new car, is to replace everything so that it is all new. A car is the sum of it's parts. Is it worth trying to fix this problem, that is a whole other matter as this problem can be a lot of little things that may cost more to fix then the car is worth.
I had the PCV valve replaced (not cleaned) last week when I got the throttle body and MAF sensor cleaned. To be honest, I haven't really noticed the problem lately. I'm going to watch it over the next couple days.

Interesting note on the "IAC valve". Today I took the car in for a front end alignment, my steering wheel was cocked about 10 degrees and driving me nuts. I also asked him to clean the IAC valve and to replace all the rusty hose clamps. (the clamps were pretty bad, some were literally falling apart when they were removed). He said he'd only charge me $20 to clean the IAC valve because it was so simple to do. After his guy finished, I asked him how the IAC valve looked, he said it was dirty, but it cleaned up fine. Looking on the invoice, he charged 79.95 for the alignment, $20 for under hood labor, (IAC cleaning??), and did not charge me for a ton of clamps. I wasn't expecting a charge for the labor on the clamps because he had previously said he would do them for free, but I was expecting to pay for the clamps (but he didn't charge me for that either). He didn't do any of the work (he's the manager). I'm wondering whether the mechanic who did the work, just failed to communicate to the manager that there was no IAC to clean, and so he just assumed it was done and invoiced it anyway? It was already past closing and they were in a hurry to get out of there. I guess that could explain the IAC cleaning mystery, but that doesn't explain why he would answer my question about how dirty the IAC valve was. I'm guessing that's just his standard reply to customers even though he doesn't actually see the work done? Little bit of fibbing going on there. :roll:

I really had wanted to see the throttle body last week after they cleaned it up, but forgot to ask. I wanted to make sure they actually removed it and cleaned it properly. As soon as I get a nice day, I'll stick a flashlight in there and have a look.
2009 Pontiac Vibe 1.8 FWD Manual Trans
FatherTime
Posts: 60
Joined: Sun Dec 22, 2019 8:24 pm

Re: RPM dip at stop

Post by FatherTime »

Just an update on the RPM dip issue. Been watching it for a few days...gone. Idles perfectly at stops. Either it healed itself, or one of the three things I had done fixed it. Cleaned throttle body and MAF sensor, and replaced PCV valve. Anyone's guess.
2009 Pontiac Vibe 1.8 FWD Manual Trans
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