Mrmerlin

Glad the engine is running as it should .

NOTE, In the last picture the throttle plate looks to be opened just hair more than the one I have if so that could be why the ICV cant lower the idle once the throttle bore gets hot it could be jamming the plate I would still loosen the 2 screws a half turn and see if the plate recenters itself

Pagnobito

I'm no expert but I don't think that is the case. I've only seen a couple of these and some in pictures which is the only reference as I couldn't find any details of how to set it apart from how visible the upper vacuum hole is. Anyway, I've done all that on a previous intake removal to check it was all correct, you can still see some blue on one of the screws from the thread lock. It's centered and as closed as it can be and the stop just touching. I've said a couple of times I had checked it. During testing the engine was run from cold to hot without touching the throttle so the plate never moved even when hot as the TPS always registered closed (idle).

It wasn't a gradual speed increase such as might be seen if as the bore of the intake expanded and let more air in, the ISV would suddenly switch from 40 odd percent and good idle to 20 odd and stick there. I could hear the sudden intake of extra air. When at normal idle and stopping air going through the venturi the ISV would increase airflow to compensate and keep idle normal, when it went to 20 it didn't do that. In other words I couldn't change idle speed by blocking the venturi hose when the ISV was working correctly but when it stopped working correctly blocking the hose changed the idle speed.

I can't explain it, they all measure the same resistance, the new ones have a larger internal opening when on the stop and smaller entry and exit bores but that shouldn't make them suddenly change position. I read that high idle could be a ISV fault but that's usually on old ones that have got stuck.


I haven't changed anything about the intake today except swapping the original ISV in and took the pictures while it was off. I think I had the cold start problem as the ISV was sticking and now it's cleaned is probably OK but a few more drives will confirm.


Thanks

Mrmerlin

I went and took pictures of my 2R throttle body it appears that its the same as what you posted



2R throttle body from a 1988 S4 this small hole is at the top edge of the throttle plate and this is what you should see if the setscrew has never been messed with


This 2R throttle body appears to have never been adjusted from when it was new

SeanR

Here's one I had on the shelf that I know is correct.

Pagnobito

Thank you for posting pictures of the butterfly which confirms that mine is as it should be.

Taguid

I think it has to do with some type of signal corruption introduced either from TPS or ISV because I too have tried two ISVs (Bosch and Lowe) with the same idle increase. Mind you I did not have the idle problem until I changed the TPS. I thought it was the ISV so I bought the Lowe to try and see if anything would change and it did not but as soon as I put the original TPS back in it now idles as it should.

matt968

I still have the same issue. Originally my problem was just like the others - it literally switches from normal idle to a higher idle (800-900) as soon as it get up to operating temperature. This is while starting it and just letting it sit to warm up. However, after replacing the venturi the idle issue would only develops after driving it a few miles to get it to operating temp. Letting it sit and idle to warm up would no longer cause the problem. Although I am not certain the venturi had anything to do with it.

In the course of trying to fix this I have replaced the TPS with 2 new Bosch units and the original TPS with no luck.

This past week I installed another new Bosch ISV and at the same time I slightly loosened the butterfly screws to make sure the blade was not binding in the bore and then retightened them. NOW the problem is back to like the original issue....letting it sit to warm up causes it to switch to higher idle as soon as the H2O gets to operating temp.
So I guess I will have to put my other Bosch unit back on to see if it has an affect on when the idle issue develops - while sitting to warm up or driving it...not that it matters since it ultimately has the same issue.
I no longer have the original ISV try. I suppose if someone had a "known-good" original unit I could try that.

FYI every hose and plastic connection is new....and like Pagnobito determined, it's not an air leak. It's literally like someone flips a switch to change the idle speed.

At a loss now.

Pagnobito

I was going to make a fly lead to piggy back onto my ISV and measure the voltage and current as temperature increases but as the original ISV works I haven't got that far. I started to fix the HVAC and just today some replacement parts arrived to finish the job.

Remember the only change I made on mine was re-fitting the original ISV which was replaced due to it not starting without throttle from cold. I concluded my original ISV was sticking and now I've cleaned it up it works fine.
So what's the difference between the original and new ISV? Well, the only difference I can see is the spring is far tighter on the new ones. Measured cold resistance is 8 Ohms on all of them.
A friend made up a circuit to test a new Lowe one he has, it likes 100Hz and draws about 1 Amp..

I'm wondering if the common link between our cars and what has to be the ISV tighter spring or the way it's driven is something weak in the circuit that can no longer drive the coil properly when it gets hot. Although I could manually set the ISV position so that theory doesn't quite hold up. If mine still had the same problem I was going to run a new lead from the LH to the ISV in case there is a weakness in the wiring causing a voltage drop.

Matt, 928intl list a used ISV for 100USD which could be your next stop or using a fly lead to measure the voltage and current to determine if the loom is suspect?

matt968

Original ISV Wanted....
Does anyone have an originally fitted from the factory ISV? It should be in known good working order.

I still have the same problem that has been documented throughout this thread. No idea what to try anymore, but since this is what fixed "Pagnobito's" thought i would try the same thing, except I no longer have my original ISV.

I checked the duty cycle of the valve with a multimeter. It does the same thing Pagnobito's did. On initial startup it holds around 45%. As H20 temp slowly warms up it drops to around 41% which keeps the idle at the specified 675 range. Then after it gets to operating temp at some point the duty cycle drops to 10-20%. As it passes through around 35% the idle increases. Which I understand is to be expected as the valve closes and then reopens to its fail safe mode in case it looses its signal.
I've installed mutliple ISV's. With one ISV I installed, it does this without driving it - just letting it sit an warm up. With 2 other ISV's I installed it will do it but only after I drive it. Today it was idling too high after driving it and so I put it in 2, accelerated to 5000 rpm then decelerated back to a stop and the idle was fine! Makes absolutely no sense.

Pagnobito

We took ours on around a 1200 mile trip to Germany and it behaved the entire time. Only problem was we hit a large dip at 75mph on the motorway near Mons in Belgium and we came to a stop, it wouldn't restart. It was our last day, on our way home so we left the car as I couldn't fix it (thinking it was fuel pump as bridging the relay didn't help). It was transported back about 10 days later and I found the wire to the fuel pump had been cut where the top of the rear sway bar link had met the body and the wire was there. I have repaired and moved the wire out of the way so it'll never happen again.

I hope you can find a good used one and it fixes your problem.


Mark on top of link showing where it met the wire

Broken wire, I have removed the outer cover, it was hardly visible as a small cut.

matt968

As a follow up, I purchased an original, used ISV (with a Bosch part # 0-280-140-515 label) and this fixed the issue.

Prior to this issue, every hose, connection and sensor was replaced. MAF was re-calibrated. Fuel Injectors flow tested and cleaned...Basically a full intake refresh.

The issue only developed after replacing the ISV. I installed 4 different ISV's - one I purchased directly from Porsche. I had the LH rebuilt. I even swapped my rebuilt LH for another LH...nothing made a difference. I smoke tested the intake to verify no leaks....I stopped counting but I know I removed that intake at least a dozen or more times.

I don't know why the ISV would drop to less than 20% duty cycle. Voltage was at 12v. Hertz was around 97Hz. Voltage drop at the ISV showed less than .1v. I did not check amps at the ISV while it had this problem. I was thinking maybe the LH was unable to drive the newer ISV's after it got to operating temp but this is "above my pay grade" for figuring it out.

Taguid

Glad you got it solved. I still have the Lowe ISV installed with my original TPS and it is back to it's normal 675. IMHO something is definitely going on in that circuit involving the new ISV's and TPS's. Hopefully someone with the right skillset will figure it out as I think this will become more prevalent.

Pagnobito

I bet some choice words happened that day when it suddenly started working properly again! I'm glad it's fixed. Now we need to find out why the newer ISVs don't work on our cars. I know other cars with Lowe ISVs fitted and working fine. The only difference I could see was the spring is a lot stronger in the newer ones. I'm not sure if the ISV comes into play properly until the engine starts warming up and the O2 sensor kicks in, at least that's when it started to go screwy on mine. I'm pretty sure the one car I know has the Lowe ISV is a non cat car although it still has the O2 sensor I think.

matt968

What's odd is after I put the replacement ISV in I reconnected the battery and took it for a drive for about 7 miles...and it was still idling too high! That's when some choice words flew.....
I drove it home, shut it off for a few minutes, started it back up and it was back to normal idle. So I drove it for about 15 miles and it idled perfect...I have driven it several times since and it has been fine.

Pagnobito

Well, my poor cold start issue has returned, it's not happy without some throttle until it's warmed up a bit.
This is the reason I replaced the ISV which cured the cold start problem but gave me another, a high idle when the engine warmed up, not an air leak. It ran fine until it warmed up and then the idle jumped 250rpm and stayed there.
I'm not going to go through all the testing I did suffice to say putting the original cleaned up ISV back on made it run perfectly and did so on a 2K mile plus tour to Germany.
I think maybe letting it sit over winter has not helped.

So now I don't know what to do, well I sort of do, I'm going to remove the intake, clean the ISV and put it back as I never found out why a new replacement gave me the high idle problem. It wasn't an air leak!
Bummer.