87 Carrera: Topend Rebuild Complete: Throttle is sticking. Is it the microswitch ad?

[BReyes]

87 Carrera: Topend Rebuild Complete: Throttle is sticking. Is it the microswitch adjustment? Tap the pedal and it does idle but as leave and go into first. Once press clutch in the throttle wants to stay high or even accelerates somewaht.

This seems to be the microswitch. Correct? What do I do with the microswitch tomorrow guys?

Thank You.

Regards,

[ChrisBennet]

If you can make idle correctly by pulling up on the gas pedal with your toe or pushing down on the throttle lever in the engine compartment the throttle linkage is probably too tight.
I've never needed to adjust a thottle microswitch but I don't get out much.
-Chris

[BReyes]

I had a similar problem, which I resolved before the motor was rebuilt. Cleaned off the microswitch and positioned it in a way that the idle problem was fixed(had a thread here but can't find it yet) It was an idle issue. The throttle linkage may be too tight? I used a tiny wire at one of the ball and sockets so it would stay on the linkage.

Throtle is sticking . Remember push in clutch nothing it stayed accelerated. It even went up (accelerates itself)

I have to immediately lift the pedal manualy to solve this problem (and allow it to drop in rpms as I shift or come to a stop light. I'm thinking the microswitch may be ok. How to check this?

[ChrisBennet]

Originally posted by BReyes
I had a similar problem, which I resolved before the motor was rebuilt. Cleaned off the microswitch and positioned it in a way that the idle problem was fixed(had a thread here but can't find it yet) It was an idle issue. The throttle linkage may be too tight? I used a tiny wire at one of the ball and sockets so it would stay on the linkage.

Throtle is sticking . Remember push in clutch nothing it stayed accelerated. It even went up (accelerates itself)

I have to immediately lift the pedal manualy to solve this problem (and allow it to drop in rpms as I shift or come to a stop light. I'm thinking the microswitch may be ok. How to check this?

With the motor off, pull on the throttle lever on the side of the throttle body. You should hear a faint click just as the throttle lever starts to move. If the throttle linkage (or cruise control cable) is too tight, the throttle return spings may not be enough to pull the throttle to the closed position. If you can push on the throttle lever and get it to bottom out and then pull it up and hear the click, that's probably your problem.

Floor mats can also cause the throttle to "stick" sometimes too.

When properly adjusted, flooring the throttle should move the lever on the side of the throttle body so it almost touches the thottle stop.

Short of dropping the throttle body I don't know how you could get the microswitch out of adjustment. The only relationships that might change with a motor R&R would be the throttle linkage between the motor and the transmission.

I would check that the throttle linkage (the part that looks like a long coat hanger wire) isn't hitting anything esp. where it goes through the engine tin.

I've seen cruise control cables get bent and interfere with the throttle return sometimes. When you pull on the throttle lever be careful not to bend the tip of the C.C. cable.

On pre-'87 cars if the you don't put the clutch cable in the right place (up against the side of the transmission) it can rub on the throttle bell crank and cause sticking. Don't ask me how I know that one.

If worse comes to worse, you can disconnnect the throttle linkage at the transmission and "cut the problem in two". You'd be able to detect if the sticking was on the motor side or the car/tunnel/pedal side that way.
-Chris

[bfegan]

Look carefully at the connection between the cruise control cable and the throttle. Where the wire leaves the cable casing and runs to the throttle, the "plastic"(?) retaining device (which fixes the distance which the wire will move) tends to crack/break. A good glue on the plastic will fix this so that the distance is correct and remains constant.

As noted above, the floor mat can get jammed under the bottom of the accelerator pedal linkage.

[Decolliber]

I had the same problem after a rebuild. When they disconnected the throttle cable, it got slightly bent, so when they put it back together the cable rubbed slightly as it went through the firewall, causing the sticking.

[BReyes]

Yes the cable may be rubbing (as it has a bend in it and the angle is ?). I will check that not rubs (hope this is visible).

I was thinking the switch may be the culprit. What is the logic of the switch. I ask to reason through this more. The click part reminds me of how I corrected a problem similar to this just prior to the rebuild.

It may be a combination of both or additional problem with throttle.

Regards,

[jbrinkley]

If you read through this you might get some more answers
http://forums.rennlist.com/rennforums/showthread.php?t=202063
link to PP post with more of same
3.2 Sticking Throttle

[bfegan]

I doubt that it is the micro switch. The micro switch tells the DME whether the throttle is closed. If the switch says "closed", then the stock chip within the DME selects the proper ignition advance and point on the air/fuel map by default. If it says "open", it reads the other sensors to determine the appropriate values. If the switch is faulty, you will have the same idle all the time (fast or slow). Yours "sticks", which would lead me to think that the switch is innocent.

I went all through this when my idle remained constant at 1800/2000 rpm. Thankfully, Steve Wong educated me on this and stopped the $$$$ hemorage of replacing DMEs etc. upon which path I was embarked.

Hopefully I have not over simplified how this all works, but I beleive it is correct.

[BReyes]

Yes, I previously resolved a problem whereby the idle remained consant at 1800/200 rpm and if I tapped pedal it settle to 880. Yes. This problem does seem to be a sticking issue.

I have to pull up on pedal immediately.

I haven't been under the car today.

Happy father's day!

[BReyes]

is the throttle cable trans to engine supposed to be straight or slightly curved?

Thanks again.

Regards,

[bfegan]

I believe slightly curved is OK... straight is better. Just so it doesn't bind.

If your car has cruise control, the cruise cable is the one approaching the trottle on its' left side,viewed from the rear of the car. The cable sheath is restrained by a bracket about 4 inches from the throttle and the wire exits its' sheath from the bracket... which restrains the sheath with a plastic piece. This plastic piece frequentle breaks/cracks which changes the distance from sheath end to throttle causing the cruise cable to bind and hold the throttle partially open. This can easily be repaired with a little super glue. Hopefully this is your problem.

The micro switch sits below the point where the cruise cable wire connects to the throttle body. If the micro switch is bad, you must remove the induction system in order to replace it.

My problem was the micro switch. I have a SW chip and Steve has built his chips to be more sensitive to readings from the micro switch than the stock chip. A faulty micro switch will be masked by a stock chip, wheras a chip programed for more responsiveness to the sensing will cause a consistent 1800-2100 rpm idle. I literally swapped out DMEs and chips and verified this.

Hope all this helps.

If its not the cabling, I'll get the specs so you can check the micro switch with a voltmeter.

[BReyes]

The cruise control plastic piece was loos and I used a tie wrap to secure it. Throtle is fine. Yes I have a chip too, and the microswitch is ok (as I had sorted [ it had debris on it and cleaning it solved the idle at 1800/200 problem) this several months ago.

The engine has a couple of hours on it now and I am off to continue breaking her in.

Regards,

[84Targa]

My 1984 Carrera was idling at 2000 rpm once it got to normal operating temperature. This post helped me figure out the problem was with a bend in the cruise control cable (I never use cruise). Once I straightened it out the problem went away. Thanks for these posts!