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I am a born again user of Pontiac Bonneville Club! I haven't been around for quite some time. I found that other Bonne forum and was having extreme difficulty finding anything and trying to figure out what was going on. I went back to Google and finally found this site again. Either I forgot my original login or we all had to create new accounts?? Anywho, I am sure glad I found this forum again.

Onto the issue(s) at hand...

My Bonne has been acting up lately and is to the point of being nearly undrivable. It has been idling erratically. At first it was idling a little high and then drop back down to appropriate idle speeds with either a motor restart or a quick goosing of the gas while in Park. Recently it was quickly fluctuating between 2000 and 3000 RPMS at highway speed. Last night I was going to head to a buddy's place and it wouldn't idle lower than 3000 RPMS. When I drove 30 MPH it was running at 4000 RPM. I quickly put her back in the garage knowing it needs some TLC ASAP.

I pulled some codes via the paper clip method this morning. It return 21 (TPS circuit - Signal Voltage High) and 22 (TPS circuit - Signal Voltage Low). It also return 36 (Transaxle Shift Control Problem).

I am guessing the TPS needs to be replaced. Anything else I should be looking at to get full diagnosis? Could a cracked vacuum line also be causing havoc?

The TPS was replace about 3-1/2 years ago by a mom and pop garage. How difficult of a DIY is this? I have a Chilton's manual, but I'll be *dang* if I can find the section for the TPS.

Marmot

It could be the TPS or maybe the Idle Speed controller.

The TPS can be easily changed by removing the throttle body. If you are good with tools, it is possible to access the two screws without removing the TB, using a vicegrip to loosen them and then turn them out by hand....providing they are not rusty.

I would look at the idle speed motor first.

Tell me more about the idle speed control motor and how to diagnose it as a potential problem. I am not much of a mechanic, but know how to follow directions.

Marmot

I made a run to the auto parts store. They didn't have a TPS in stock. They will have one tomorrow. I am planning to get a TPS, IAC, and throttle body gasket. I hope this takes care of the high idle speed.

Marmot

Considering two of the codes are both extreams of TPS readings, I'm betting the TPS sensor is toast or the wiring going up to it has an issue.

Do you have a scan tool that gives realtime values off the sensors?

If you do, plug it in and work the throttle by hand while watching the % TPS

Marmot wrote: My Bonne has been acting up lately and is to the point of being nearly undrivable. It has been idling erratically. At first it was idling a little high and then drop back down to appropriate idle speeds with either a motor restart or a quick goosing of the gas while in Park.
I pulled some codes via the paper clip method this morning. It return 21 (TPS circuit - Signal Voltage High) and 22 (TPS circuit - Signal Voltage Low). It also return 36 (Transaxle Shift Control Problem).

Definitely a fried TPS. This is exactly what happened to me. Restarting/goosing worked for a short while but eventually it just kept getting worse. I finally got an SES for it, and it returned me a Code 21 also. Unplug the TPS's electronic plug and see if it starts normally. Mine did, and I reattached and disconnected over and over to make sure. The TPS is a DYI job pretty easily, but other than not having cruise control it didn't seem to hurt me to drive for a while with it unplugged. I don't think you need to replace the IAC unless the new TPS doesn't fix it. Good Luck!

EDIT: I can't quote properly. Sigh

I don't have access to a scanning tool. The local parts store doesn't have one for use either. I somewhat live in the sticks. It is not very convenient to drive to hopefully find an auto parts store with a scanning tool available for use.

Depending how difficult the tear down and reassembly of the throttle body is, I might skip replacing the IAC. If I have problems along the way, I will probably replace the IAC just to make sure I have my bases covered.

I plan to clean the throttle body and MAF sensor while I have things tore apart.

Marmot

I just came in from the garage. I unplugged the TPS and it idled close to the speed it should be idling. Is it a safe bet to forgo the IAC?

Marmot

Yep. Real safe bet. It wouldn't hurt to be replaced if you already bought one but I would say you don't have any issues with it. Those darned TPS's. As I said, it should be OK to drive without the TPS plugged in for a short time if you need to go somewhere to get one or need to make a run around town. I've known people who unplug their TPS's permanently on motorcycles without issue. I'm not sure of what it may hurt in a car other than disabling the cruise control and keeping a constant SES light.

Another quick item....

As I previously stated, no one will ever mistake me for an auto mechanic. I have read to use the brake booster vacuum line for a Sea Foam treatment. In the attached pic, have I properly identified the brake booster vacuum line?



Any concerns of doing a Sea Foam treatment with the TPS disconnected?

Marmot

edit I: hhhmmmm....the board doesn't automatically resize pics to an appropriate size?

edit II: resized pic

Yep, that's the booster vacuum line. And I seafoamed once with my TPS disconnected. No issues. It took me a couple seconds to get her to fully turn over but once she did I smoked the neighbors out. That's normal of a dirty car, though. Nothing to do with the TPS

Just make sure when you unplug it the engine has been running at reg temp and you plug it with your thumb before it stalls. otherwise it turns into a dance between the ignition and booster line re/disconnecting.

correct. seafoam should be fine with no TPS, i don't see why it would matter

After seafoam, you may have to replace plugs and the O2 sensor.

And Seafoam won't possibly be able to help clear up any IAC (idle air controller) issues. Only a throttle body removal and cleaning can.

Let's diagnose one thing at a time without introducing other issues.

Oh......I didn't intend a SeaFoam inoculation to solve my idle problems.

As long as I will have the throttle body off, I figured I would run some SeaFoam through the vacuum line beforehand. When I take the throttle body off to get at the TPS, I plan to clean it thoroughly (per the instructions in the TechInfo section).

Marmot

Just an FYI, you don't have to remove the TB to change the TPS.

willwren wrote:Just an FYI, you don't have to remove the TB to change the TPS.

Thanks for the heads up on that.

Marmot

Marmot wrote:

willwren wrote:Just an FYI, you don't have to remove the TB to change the TPS.

x2
I may be a village idiot, but removing the TB (for a leaky gasket) was a lot bigger PITA than just diving into the TPS as is. I'd try doing the TPS w/everything intact and save removing the TB as a fallback. Also, be advised that the IAC has a measurement/adjustment before inserting the new one.

Finally, as everybody else has stated the TPS definitely will cause these symptoms. Mine also induced trans shifting issues.

I am passing on the IAC for now. I decided against spending $70 (or was it a $105) on a part that may not be having issues.

I may pass on removing the throttle body also if it is a PITA as I am not the most skilled mechanic.

Marmot

You'll need an offset screwdriver or mini-ratchet set with the proper bit.

If you do decide to take off the throttle body, make sure you pick up a new gasket before taking things apart. The gasket will need replaced. Pretty sure it mentions that in the Techinfo somewhere near the bottom