Stange idle problem

arnebret · 03-23-2002, 06:45 AM

Hi,

Here's another of my strange, small problems:
when i start my engine cold the engine does a nice idle of 900rpm. But when i drive the car real hard an fast for a couple of minutes and the engine is real hot the idle is sometimes somewhere at 1200rpm and just won't get any lower. I already did the idle adjustment as it should (with a hot engine disable idlestabilizer and turning bleedscrew on throttle body as far in until it reaches the desired rpm, in my case almost all the way in).
One thing i can remember is that i cleaned my throttle body a few weeks ago. Maybe it's out of alignment or someting?

Any ideas?

Thanks!

PS: the car also is very sensitive to suddenly letting go of the accelerator when driving. It jumps a bit when letting go or suddenly pressing the accelerator. Of course, more in the lower gears, but it's also noticable in 3rd and 4th.

Lawrence Coppari · 03-23-2002, 10:43 AM

If it didn't do before what is doing now that you have taken it apart and cleaned it, it sounds like a vacuum leak to me. I'd take it apart once again and reassemble.

Did you remove the electric switch? I did that once when I sent my throttle body away to have it reamed out. I put it back out of adjustment and could not control the idle. Turned out the switch was preventing full throttle closure. I could see light around it when I held the throttle body up to a window.

arnebret · 03-23-2002, 11:59 AM

Yeah, i got the same. I can see a bit of light coming through as well. Is the switch holding it back? It does seem the plate can't completly close. What do i have to do, is this a specialist job?

Lawrence Coppari · 12:27 PM

When I reinstalled the switch I merely set it up wrong and it prevented the throttle from fully closing. I could see a sliver of light all the way around the butterfly. There is also another throttle stop. It is located on the side opposite the switch. It should be the thing that stops the throttle or so I think. When properly adjusted, I could see no light around the butterfly and could hear a click when the switch opens or closes (I don't know which way) just as the throttle fully closes. The switch tells the DME to shut off the fuel (when throttle is fully closed) until the rpm gets below 1400.

I would think you could adjust it properly yourself. Just set the throttle stop so the throttle contacts it when the throttle closes meaning the butterfly is perpendicular to the axis of the body (no light or minimum light visible around butterfly periphery). After that is set properly by using a screwdriver on the bolt and tightening the locking nut, then do the electric switch by loosening the two set bolts and fixing it so you just hear a click when the throttle completely closes. This is much easier to do with the throttle body off the intake. In fact, I cannot get at one of the switch bolts unless mine is off.

Don't know if this is the party line on how to do it but it works for me.

arnebret · 03-23-2002, 01:33 PM

Mine does that click right before it fully closes. It seems the switch is installed ok but i will have a look at the screw that stops the butterfly from closing any further.

arnebret · 03-30-2002, 01:19 AM

Well, i had a look at the throttle body and noticed some light all the way around. I can't seem to get it into a full close. But what i also noticed is that sometimes all of a sudden the engine, at idle, revs up to a steady 2300rpm or so, and when i push on the side of the throttle body (for example on the throttle switch), rpm drops to a nice stead 900rpm. There must be something leaking. Might it be the rubber seal that has to make the connection to the intake manifold air thight??

DennisR_944 · 03-30-2002, 02:33 AM

You might want to check to insure that when you let off of the accelerator. the accelerator cable is adjusted so the throttle is completely closed. I fought an idle problem for days before I realized that the cable was just too tight. Good luck.

arnebret · 03-30-2002, 07:18 AM

I just don't get it.

I checked all things: throttle cable, throttle body, all hose clamps and verified some readings from the KLR and DME. Everything within factory specs so throttle switch is okay. Everything is airtight, and the throttle body is fine as well. And i must say the car is doing fine.. also in the more regular boost levels (1.2-1.4bar). Nothing seems to be wrong. But at higher boost 1.4 to max the engine does everything fine, turbo spins up to 1.8bar and the car accelerates fast and at random rpm's the engine just surges, picks-up, surges, picks-up, it bounces up and down. To be honest, i don't think the problem is in the air supply. I checked it all the way around and all seems tight.

The only thing i'm not to sure about is that banjo bolt that goes in the before-wastegate tube. What is it's function, i never checked what it does and if it's set properly.

Besides that, i can recall a clear hose from the wastegate to some valve (timing valve??) that needed replacement, it was still okay, but needed replacing. I know there is another one going to the KLR, but this is coming from the intake manifold. Maybe one of these hose has finally given up and giving wrong readings to the computers causing this problem.

Another thing i can tell you is that my car just had a new clutch and torque-tube, are there any sensor or parts in that area that might cause the engine to do this at high boost?? (not likely)

Anyhow, all opinions are welcome!! I really want to fix this..

DennisR_944 · 03-30-2002, 11:19 AM

If you just had a clutch done, you may want to check all of your grounds, especially the main one going to the rear of the engine. Bad grounds can cause all kinds of funny readings, etc.

Flight 951 · 04-01-2002, 11:27 AM

I recently had a throttle position switch act up on my car. One day, the idle started fluctuating between 1200 and 1800 rpms consistently. Vroom. Vroom. Vroom, at stoplights. Apparently, the electronics in the TPS go bad, and you may be able to check this by popping the hood and tapping firmly with your finger on the TPS while the car is acting up. My car stopped doing this after I tapped it. I'm now waiting for a new TPS now, since I guess the old one was on its way out. My car has 82k miles. Hope this helps.

arnebret · 04-02-2002, 11:10 AM

Roger, this is the exact same problem i have. I did some check-ups and it MUST be that switch. The KLR on a turbo uses a reading from that switch to see control all systems concerning boost. If it's not connected it only allows 1.2bars boost. When on a higher boost level the reading from the switch is suddenly lost fuel will be cut right away to protect the engine from either overboost or other unforseen trouble. Quite a nice system, if all the input is ok at least

robm-951 · 04-02-2002, 11:53 AM

Arnebret,

On the throttle body, the throttle shaft actually rides on needle bearings pressed into the throttle body. These needle bearing have lip seals on the outsides, could you have removed one of them while cleaning? If this is the case, I'm not sure if you can get the bearing and seals seperately from porche. I'll check on PET tonight. I meant to do this a while ago, because mine where shot and leaking under boost. Since I was in a pinch, I went to the local hardware store and bought a couple of o-rings. I then pulled the seals out of the bearings and replaced them with the o-rings. (the seals sit in a groove in the needle bearings). They ended up sealing great and I ended up forgetting to ever check if the correct parts are availible.

later,
Rob

arnebret · 04-02-2002, 12:05 PM

Well, i'm not quite sure if i understand what you mean. I checked the PET system and there is only a limited amount of stuff you can buy seperatly for the the throttle housing. I might do with a new sealing ring by the way... I have no idea if this is one of the sealings that have to be 'ALWAYS' replaced.

arnebret · 04-03-2002, 12:46 PM

I checked the body again and indeed i did notice some sort of O-ring at the right side (the one without the switch). If there SHOULD be one on the TPS-side between the TPS and the body itself, then i might have found my problem here... There isn't any. It would explain quite a lot.. i will take out the body again this weekend and see if i can get me an o-ring at a good hardware store that properly fits. There isn't a factory Porsche replacement... at least i can't find it in PET

robm-951 · 04-03-2002, 05:53 PM

Arnebret,

There is suppose to be one seal on each side of the throttle shaft. The original ones are a lip seal, but the o-rings I found worked great. I did have to pull the throttle shaft out to put them in, but its fairly easy. Just be sure to get the throttle blade centered in the body before tightening down the screws. This way the throttle blade seals off the throttle body opening like it should.

Later,
Rob

arnebret · 04-05-2002, 01:45 PM

Hmm, i took my throttle body apart as far as i could. I only noticed a couple of washers and actually just one o ring. The only rubber ring i could find was the one that is on the TPS and connecting (sealing) the throttle body. I can't find any other rings or even washers.. is this normal?

As english is not my first language please explain the lip-seals... what kind of seal is this?

robm-951 · 04-05-2002, 05:58 PM

Quote:

Hmm, i took my throttle body apart as far as i could. I only noticed a couple of washers and actually just one o ring. The only rubber ring i could find was the one that is on the TPS and connecting (sealing) the throttle body. I can't find any other rings or even washers.. is this normal?

Mine had one seal on each side (one on the TPS side and one on the Throttle cable side). To see the one on the throttle cable side, you must remove the throttle shaft (the part that turns the inside of the TPS), to remove the throttle shaft, you must first remove the throttle blade (the large brass disk that varies the amount of air allowed through the center of the throttle body). Did you take it apart this far? The throttle shaft rides on needle bearings (one set on each side of the throttle blade, pressed into the body). Each of these needle bearings has a lip seal that seals against the throttle shaft. The seals are located on the outsides of the needle bearings.

Quote:

As english is not my first language please explain the lip-seals... what kind of seal is this?

No problem, English is my first and only language, and I still haven't mastered it. A lip seal is a seal that has a rubber lip that seals against another surface. An example of this is a wheel bearing seal. In contrast, an o-ring is a seal that has a round cross section.

Does that make sense?

Rob

arnebret · 04-06-2002, 12:23 AM

Yep, i took the complete throttle body apart. Meaning, i took at the shaft, the blade etc. The only thing i found on the outside of both needle bearings are two regular metal washers.
It doesn't seem to really make this airtight.. but it seems all factory stuff...

robm-951 · 07:31 AM

Quote:

The only thing i found on the outside of both needle bearings are two regular metal washers.

Maybe there is a differrence between our two cars because of the years, Mine an 86

When you say regular metal washers, are they actually washers that you can take out or do they appear to be pressed into the throttle body? On mine, each side had the needle bearings that are encased in a shell that get's pressed into the throttle body. The shell on mine had a space where the seals went. Let me try and draw out a cross section for you. The dashed lines would represent the needles, and the "o" was where the original seals were. The straight lines represent the casing.

|---------|o|

Either way, your throttle body should be pretty well sealded. Typically, manufacurers will just use a bushing in the shaft because a properly fitted bushing provides a good enough seal, but with needle bearings, a seal of some sort is needed because the spaces between the needles and the shafts would allow too much air to enter.

Rob

arnebret · 04-06-2002, 08:03 AM

Well, i now know exactly what a lip seal is and saw that there where two present on each side. I put the whole thing back again and tested it by just blowing in it. There was almost no air leaking through the two bearings. Most air was just bypassing the plate. I adjusted the plate such that as less air as possible could pass. But still the plate isn't a 100% fit with the housing. It seems the housing is a bit worn out because the plate wasn't properly adjusted before.

After some re-adjusting etc. etc. i finally found the less worst position. I also fixed any play that the shaft had in horizontal way. I put it back in the car and can now get my car to a nice steady 900rpm (about). But the idle screw is almost all the way in... it seems the house needs to be replaced if i wish to get it all back. For now (and the next months), this will do fine... the car accelerates fine, has an idle of 900rpm and is functioning properly.

Thanks for all the help!!! I think i found the problem and fixed is as much as possible...