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Old 12-10-2011   #1
wilkink
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Weird Problem

Hoped in my car one day and something wasn't right. Off the bat it felt fine until I gave it some gas. After I gave it gas, it felt like either the throttle was sticking or the cruise control was stuck on. For example, if I got the car to 30mph, the car would stay at 30mph even after I took my foot off the pedal. When the car sits at idle, it also idles higher than usual at around 1500rpm. I unhooked the cruise control and WD40'ed the throttle a tad. Still have the issue. I also cleaned the IAC about two months back, so I don't believe that is the issue, if it could be considered a culprit. If anyone can help, it would be much appreciated. Also, if you need any more information, I will be glad to give it to you.
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Old 12-11-2011   #2
merc3065
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Re: Weird Problem

have you adjusted the minimum idle set screw?
check to make sure that the throttle is returning properly and not sticking slightly open. If it is, the throttle return spring may need replacement.
Check the accel pedal and make sure its not sticking either.
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Old 12-11-2011   #3
wilkink
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Re: Weird Problem

Thanks for the response. Can't say I've set the minimum idle set screw yet. I will also check the other two tomorrow when I get around to checking the TPS. Thanks for the recommendations.
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Old 12-16-2011   #4
Badassbird
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Re: Weird Problem

Check for any vacuum leaks especially at the Brake booster vacuum tube. Cleaning the IAC cannot fix an electrically malfunctioning IAC Motor so the IAC is still a great possibilty and of course an mechanical linkage issues as mentioned by the other members.
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Old 12-26-2011   #5
red88tagta
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Re: Weird Problem

Year, model and engine specs and any sel codes please.
With that info we will be able to help further.
First disconnect the cruise control cable to see if that is the culprit.
Second disconnect the accelerator cable to make sure there is not a binding issue.
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Old 12-26-2011   #6
TTOP350
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Re: Weird Problem

Also another thing to look at is a dirty oily gumed up T-body. If it is, remove it and clean it up..
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Old 12-26-2011   #7
YumikoGTA
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Re: Weird Problem

Make sure that if you remove the throttle body to clean it, that you remember exactly how all the hoses connect back to it. Reinstalling incorrectly will cause the engine to have a lot of performance issues. Also make sure that when you reinstall, that the gaskets are all properly installed between the parts, or this could cause a vacuum leak while the engine is running and create problems for the engine. Also before you use any solvants, make sure that they are sensor safe, because if the sensor coatings get damaged, this will ruin the sensores and the sensors will not provide accurate data to the computer, and if the data provided to the computer is inaccurate, you will forever have issues with your engine running correctly or at the specifications as it was designed. Some carborator cleaners and other types of harsh cleansers will damage sensor coatings, so make sure that you get a sensor safe type of cleaner. Sensors are sometimes expensive and now with the ones that are on our GTAs, they can be sometimes harder to find. Also you save a lot of time and effort not having to figure out which one is damaged. I would say that the best way to do it is to minimize some and to completely eliminate all of the unnecessary risks involved. Doing so has seemed to make working on my GTA a much more pleasant experience, which I am sure you would agree with.

Lastly, if you remove the throttle body, if you do not have to remove the Throttle Position Sensor (TPS), just make it easy and do not remove it. Because to reinstall it correctly so it will send the correct signal to the computer, it has to be properly adjusted when reinstalling. You can not just reinstall it without doing anything else. And when the Throttle Position Sensor is not properly installed, it will cause a lot of issues with the engine. If the TPS is incorrectly installed, one of the things that this will cause the engine to do is run as though you have your accelerator pushed in a little bit when actually you are not pushing the accelerator at all. This is the one that I know about but I am sure there are other issues that an improperly installed TPS will cuase.

Good Luck,

Yumiko
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Last edited by YumikoGTA; 12-26-2011 at 05:06 PM.
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Old 12-26-2011   #8
wilkink
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Re: Weird Problem

Thanks a ton for all the information. Really appreciate it.

As for red88 - I have exactly what your name implies, a red 88 GTA with the 350. The car is not throwing any codes and I the first thing I did was disconnect the cruise control cable and it didn't help. I also took the accelerator cable off and pulled on it a few times to see if there were any issues and everything seemed good there. Also put a little WD-40 on there to keep it smooth.

I took off the throttle body and the plenum and cleaned them both up with some sensor safe cleaner, as Yumiko stated. The plenum was a tad dirty, but the throttle body looked pretty good. I also bought a voltmeter to check if the TPS was installed correctly, but can't get a clean reading out of the thing. It works when testing a battery, but it bounces around when trying to test the TPS. So I gave up on that after three hours of messing around with it.

I have also had another issue that I cant figure out for the life of me. Car requires a few pumps of the gas pedal to start up. Fuel pressure is fine, but when I turn the key I have to press the gas pedal a few times for it to start up. After it starts, I have to keep the car running for about three seconds using the gas pedal, or else it dies on me. Not sure if these are connected or not, but any information regarding either one of these would be a big help.
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Old 12-26-2011   #9
rhomanski
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GTA Year: 1988
GTA Engine: 350 TPI Automatic
Re: Weird Problem

The throttle position sensor should not bounce around on your meter. If you maintain good contact with the sensor. You should be able to watch the resistance smoothly rise and fall as you move the blade. Bouncing would suggest the sensor internals are corroded and needs to be replaced. It can cause the problems you are having.

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Old 12-27-2011   #10
red88tagta
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Re: Weird Problem

rhomanski is probably dead on on this one. Still suprised that the ecm isn't throwing up a code. BTW whens the last time you checked/changed the fuel filter? Do you have a constant fuel pressure?
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Old 01-01-2012   #11
wilkink
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Re: Weird Problem

Sorry for the delay, but replaced the fuel filter about four months back. Fuel pressure is good. I have it set at 44. I am pondering buying a replacement TPS. I have a stock number of TH37 off of Summit. Does anyone know if this is the correct one?
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Old 01-02-2012   #12
YumikoGTA
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Re: Weird Problem

I am not so sure how the aftermarket TPS is. Sometimes electronic sensors that are aftermarket do not work so well, not all of them but some of them. I can remember some of the members on this site mentioning in the past about the aftermarket electronic ignition modules not working so well.

Would too much fuel pressure cause some issues?

Good luck and hope that you figure out what the issue is.

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Old 01-02-2012   #13
rhomanski
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GTA Year: 1988
GTA Engine: 350 TPI Automatic
Re: Weird Problem

For stuff like that pony up and buy GM. You'll feel better in the morning.

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Old 01-17-2012   #14
wilkink
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Re: Weird Problem

Finally got around to checking things out again. I put off buying things until I figure out exactly what it is. I reset the IAC and tried to do the TPS, but still getting crazy readings. But I do believe I found out what is causing the cruise control issue.

I will try to explain this to the best of my ability. Sometimes after I rev it a couple times, I believe it is the trottle that sticks. I believe this to be true because there is a gap between the minimum air screw and the part of the trottle that usually returns to the screw. Sometimes it returns all the way and sometimes it gets stuck a couple cm away. Hopefully you know what I'm talking about. With that said, I tried spraying the hell out of it with WD-40 and then tried it again with no positive results. So does that mean the throttle is sticking or the spring on the throttle has gone bad/doesn't work correctly?
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Old 01-18-2012   #15
merc3065
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Re: Weird Problem

Probably need a new spring on the throttle blades. I don't know how to repair those.

Maybe a GM tech would know or someone else on the board.
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Old 01-18-2012   #16
george88gta
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Re: Weird Problem

I believe that most of the joints are riveted or swedged, so it wouldnt be easy to repair. Here is one option http://www.ebay.com/itm/310256077809...84.m1438.l2649
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Old 01-19-2012   #17
wilkink
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Re: Weird Problem

Thanks for the ideas. That's a little bit more money than I would want to spend at the moment. May have to find a way to somehow rig something up for a short time. I think it is the spring after reading a few threads over on thirdgen.
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