gtroth

I would definitely believe that it might overheat and fail. Carbonrevo said it needs heat to operate properly.

Luis de Prat

Isn't that how it feeds back to the DME in the 16V cars?

gtroth

Post 17 here shows the schematic - don't see a temperature connection to the DME (signal going off to the right goes to the ignition switch):

https://rennlist.com/forums/showthre...ght=icm&page=2

This schematic is from the '87S. For '88S, and the S2's, they change the name from "ignition output stage" to "ignition final stage" for some reason (same schematic).

jabbawok

The Heat conducting paste is to help conduct the heat away from the power transistors (which get hot in operation) to the big lump of aluminum it's bolted to.

SecaBlue

Just wanted to revive this thread. It seems my S2 has the same issues, and wondering how the OP got on?

I have pulled apart the AFM, cleaned and readjusted the arm onto a new track, then I replaced the ICM, and also O2 sensor... but still I get the bunny hop at 2000rpm when feathering the throttle to cruise. I have also cleaned all the grounds I can find.

Any other input?

aussie944cab

Check the operation of the TPS, especially the Idle switch

SecaBlue

Funny you mention that... as I just spoke to the original mechanic who worked on the car for the last 15yrs - he also suggested I check it.

As I know the Idle Valve switch is used upon cold start (and we still have cold days here in Sweden), I started the engine and then disconnected the plug of the IVS... the engine immediately spluttered and dropped rpm, not happy. Reconnected and instantly it jumped back to normal cold start idle. So that seems to be opening and closing fine. The only very odd byproduct was that the engine began to overheat at idle (over the 10-o-clock mark), and settled down once driving - even though it never has before and I have new thermostat. Weird. But since this idle valve is also used at higher rpm, I decided to drive to the shops with it disconnected to see any difference, and from the shops home I reconnected the Idle Valve, and as far as I can see, it didn't make any difference apart from the over heating at idle didn't happen, as the cooling fans kicked in before the temp reached 10-o-clock (usually kicks in at 9-o-clock or just above). Normal temp sits at first mark (approx 8-o-clock).

Before removing the IVS, I am going to give all the electric plugs a clean with electrical contact cleaner and see what happens

Luis de Prat

Is the Idle Control Valve air tight? Pulling it and blowing into one end while blocking the other with your hand, do you get any air leaking out? If it leaks, you need a new one from Bosch. They can be resealed, but it's a hack. BTDT

SecaBlue

Thanks for the idea... I will have to check

SecaBlue

So after an epic hour or so, and removing the AFM for more space, I managed to get the damn ICV out of the car. Before you say it, yes... at first I did just disconnect the intake pipe from the air intake, connect some old garden hose (fits right in) and blow... hearing a very very slight leak, lead me to remove the whole thing to see if it was the pipes of the ICV module.

I cleaned out the pipes and the ICV with acetone (can't get carb cleaner here in Sweden off the shelf) by letting it soak inside a while, and a whole heap of dirt and grit came out with the acetone a brownish colour. Flushed again and more dirt out... and again until nothing came out. Then blew again through and heard a very very slight leak, so sprayed with soapy water but no bubbles. At this point I gave up, with the thought that the leak is so minor it seriously could not be causing so much issues.

Then I wrestled the ICV back into place with my specialised tool called 'no-more-knuckles' and reconnected. Clearly the clean of the ICV changed things, with the cold start far quicker, and more response through the revs. Since the AFM was also out, I gave the throttle body a clean inside as well.

Meanwhile, not sure if it helped, but I also cleaned all the injector electrical connections, and tightened up the throttle cable which I discovered through all this was very slack.

Verdict. With the combination of a clean ICV, throttle body, injector connectors, and much sharper throttle response from the accelerator, the car is running much better. As for the bunny hop, it is still there, but I really have to provoke the throttle badly with a rough foot to feel it. The tightening of the throttle cable also reduced about a cm of null accelerator movement from idle or coasting which gave far more accuracy in the throttle being opened or not.

curtisr

A most frustrating problem - believe me I know. After checking the compression, performing a leak-down test, a vacuum test (with smoke), adjusting the AFM (new wiper arm track), cleaning the fuel injectors and more, this left me with the fuel pressure damper and fuel pressure regulator. If you can borrow a fuel rail you might have some luck.

SecaBlue

Did that solve the issue?

curtisr

The damper is in the mail. Give me til next week to do the repair and get to the track. Yes, it is a track car (see avatar).

SecaBlue

After I cleaned the ICV a few months ago, I finally managed to get a new TPS fitted by my PC... once they had the idle tuned in, it is running a little better. Much more stable idle when warm, but didn't fix the slight bunny hop. Next maybe I clean the DME connectors?

SecaBlue

How did you go?