rumble-b

Hi, I own a 1986 Trans Am with a 305V8, and 5 spd. It has approx. 153,000 miles on her. I've done the clutch, water pump, alternator, retro the a/c, and also a new carb. Let me give you a little history:
She's always run great, really no problems to speak of. Over the summer I started driving the car a lot more, and noticed one day that the idle was staying around 1100-1400rpm when you had to stop in traffic. It would vary between those two figures everytime you would stop, and sometimes would go down to 700rpm where she always had before. When it did this you could sometimes hit the gas and the engine would drop the idle down to around 700rpm. I checked under the hood, and checked the carb settings, nothing had changed. So I kept driving it for a while and it was still doing the same thing. When it does stick in the high idle you can actually see that the throttle lever is not touching the curb idle screw and the ics solenoid is not holding the throttle up. I spoke with a few people and I thought maybe it would be best just to change the carb and replace it with a new one. I thought maybe the tps or the other sensor in the carb was going bad. I replaced it, but it didn't make a difference. I have a lot more power going down the road, because it is a new carb though The other thing that I have noticed since this problem has arrived is that when you start her up at cold idle, she would also go to 1800 rpm and go into her usually warm up mode. Now when you turn her on she won't go instantly to 1800 and will go to approx. 1500 and may drop down and then go up to 1800 with an occasional jump in rpm of between 300-400. I have to tap the gas to keep it from going to high.
I also brought the car to a well known person in the area that can usually figure out these type of issues and has worked on chevy motors for many, many, years....He said it seems like it is another sensor/solenoid somewhere else on the car that is telling the computer to high idle when you come to a stop. He wasn't sure....I've also checked all of my vacuum hoses and everything is in excellent condition.
So, my question is could it possibly be like an oxygen sensor, coolant temp sensor, etc.? I'm kinda at a loss and really want to fix this.....I've read the other posts but nothing has hit mine issue on the head as of yet.

sellmanb

Well firstly, Welcome to the Boards

Now if you havent ever replaced your O2 sensor, or CTS before in the 15x.xxx miles that you've owned it you should do that anyways! But if you have, check the voltage on them and make sure they're getting the right volts at the right time, and what their volts are when your engine is "hiccuping", this could tell you something.

You said it does it in closed and open loop though, so the only thing that I can think of is that the TPS needs readjusted thoroughly. Even though you've replaced it, it might not have been installed properly. Most the time we are our own demons.

I'm by no means doubting your mechanical abilities, I'm just stating that you might want to double check it

You might want to look into these two things on this page in the tech articles

LINK

Hope this helps you out!

rumble-b

CTS --don't mind me, but i can't think of what that is....I'm used to the older cars.....I had a 70 AAR Cuda before this one....it was pretty easy to figure out, basically motor and carb....the electronic controls have me frustrated!

Oh, BTW I replaced the whole carb and called their tech line....they said the TPS was installed to the correct readings when the refurb. them. But do you trust something like that.......and the other thing was that the car started doing this with the original carb. So that is why I'm searching for something else.

Thanks for the response

rumble-b

CTS--Coolant Temp Sensor

I read some other threads with almost the identical problem....so I'm going to go out and check for the sensor with the yellow and black leads. I believe it located in the front of the engine, kinda offset to the drivers side....

Vader

The only problem with that theory is that the idle RPM is not controlled by the ECM on the E4ME carbed engines. Idle speed is solely a function of the throttle position. Throttle position is affected by the high idle cam on the choke, the curb idle stop screw, ISC solenoid, and possibly binding of the throttle shaft and/or plates. The ECM controls none of that.

When installing a new or reman carburetor, it cannot simply be bolted down and started without having to make some adjustments. The high idle cam, curb idle (and therefore TPS), lean and rich stops for the mixture control solenoid, and mixture control solenoid will usually require adjustment. All that needs to be done with the engine at normal operating temperature.

Actually, I'm a bit surprised that the Tech Line of the reman company would make a statement like that, since the curb idle RPM almost always needs an adjustment, and that directly affects the TPS output voltage.

rumble-b

The tech line did say that the TPS is not supposed to be touched, and they did mention that the curb idle screw might be out just a tad....
I've been looking for something binding on the carb itself, but I don't understand why it started doing the same thing with the old carb as well. If there was something binding I think I would of gotten rid of the problem with the new carb.....???
I did go and get a coolant temp sensor and installed it. The original one was pretty beat up....it seems a little better, but it was still idling a little high when you come to a stop. If you hit the gas real quick it will drop down to 700rpm. This has me mystified.
Also, I've only owned the car for about 3 years now. I'm the 3rd owner. The last owner told me everything was original in the car and I think he was right, including the oil and the gas....but once I did the routine maintenance on it, it ran great until this started......
If I remember correctly this car did this one other time over the summer and I tried adjusting the curb idle down.....didn't make a difference and one day while I was out I came to a stop and she stalled right out. I restarted her and stalled again...luckily I was able to get to a gas station and borrowed a torx bit and adjusted the curb idle up to where it should be and she ran fine since......
so it's back to being stumped about what is wrong with her....

rumble-b

I also brought the car and had the timing and everything else set.......they even thought something else was causing the prob....

rumble-b

Ok, here's the scoop, I've been out looking at everything...trying to see if anything is binding....I took off the air cleaner and turned the car on.....She will idle at 700rpm. If you move the throttle body fairly fast she will go right back down to 700 rpm. If you just so ever lightly touch the throttle body she will stick around 1000-1100 rpm. To get it to idle low again you either have to move the throttle body (like tapping the gas peddle) or you have to take your finger and move it back down to touch the curb idle screw. There is nothing binding in this area....I checked it thoroughly......so this is what I have found but I'm not any closer to fixing the problem.
the return spring is plenty strong as well.....so what else can it be???

sellmanb

that had me thinking return spring as well. did you try using a dab of grease around all the parts something might get a little metal-on-metal clashing? That's the only thing I can think of. As for why it's doing the same thing as when you had the Q-Jet... I dont know.

For ***** and giggles, you should atleast check the voltage to the TPS and make sure it's at it's correct spot at the correct time (check the link I gave you above).

I am becoming stumped as well lol. Maybe you have a weak ground connection or something? Never hurts to clean off your grounds and make sure they have good contact.

rumble-b

Yeah, I did the grease thing.....that didn't work....
The new carb I got is a Q'Jet. It's the same thing that was originally on my motor....
The thing I did notice is that the throttle lever doesn't stick at all when the car is not running.....it moves free and clear. So it's definitely something that the computer is doing, or a leak, or a faulty sensor.
I'll check the TPS unit today.....see if that is acting funny.

RB83L69

When the car is not running, there's no vacuum.

When the car is running, there is vacuum.

If the throttle plates each have an area of 1 sq in, (don't know offhand, just need a reasonable approximation for purposes of illustration) and you have 15" of vacuum (½ atmosphere, or about 7.5 psi) then there's about 7.5 lbs on each blade, or about 15 lbs total of force, trying to suck the throttles down into the motor. That's 15 pounds of side load on the throttle shafts with the engine running, that's not there with the engine off. That's why they stick.

It has nothing to do with computers, sensors, the TPS, or anything else of the kind. It's not voodoo or black magic (as if anything to do with the ECM would even fall into that category), it's just a car. No need to invent wild guesses like that, that have no basis in reality.Sounds like you're missing one of the return springs that your car came with. There's supposed to be 2 of them.

Add the other return spring that's supposed to be there.

You'll also find, the little "kicker" solenoid that's on the side of the carb, should be activated whenever the HVAC controls are in a position that calls for the compressor to operate; that would be Max A/C, A/C, Bi-Level, and Defrost. If your HVAC control is in any of those positions, it will operate the solenoid. The idle should go to around 1100-1200 RPM with the solenoid engaged and the compressor disconnected.

rumble-b

I do have 2 return springs on the throttle body.....sorry forget to be specific

Vader

So, have you looked into that potential throttle plate binding yet?

rumble-b

So what is the best way to check for that....I'm learning as I'm going