S5 Turbo 2 High idle (1400rpm) when hot after touching air filter box
 

Hello everyone

I almost finished restoring the A/C system of my S5 Turbo 2 Convertibile.
For making a perfect job i replaced all the o rings of the A/C system.

Problem is that for removing tha A/C high pressure pipes that are under the air filter i removed the air filer box (and the hose connected to the air pump) and then the first part of the "S "big hose that go to the turbo. Also i removed the little hose connected on the side of the "S" big hose that go to a sensor.

When i remounted all the items and i started the car, first thing i noticed it's that the engine warms very very slowly and the temperature gauge doesn't reach at all the correct working temperature (it was not fully on the middle of the gauge but it stays a little lower). Second thing i noticed it is that when the engine is hot idle stays at 1400rpm.

Then i checked for vaacum leaks and carefully i unmounted and remounted all the items i took off the first time and i didn't find anything wrong.

My engine "was" perfect. Only things i touched under the hood is the AC system (all the pipes and the A/C compressor), spark plugs and nothing else.

Can you help me?

I read that this issue can be caused my the air flowing sensor that is under the air filter box but apart removing the air filter box i didn't touch it.

Latest thing i noticed is that now the car lost some fire (rough idle but not always)

What can be wrong?

Thank you very much for your help! :)

Anyone?

So how did you "check" for vacuum leaks? It sounds like you just did a visual inspection, which is worthless.

There's several techniques, such as pressure testing ("boost leak testing") and spraying carb cleaner around the engine while running and checking for changes in idle.

Personally, I bet you have a tear in the TID (turbo inlet duct) which the big S pipe you describe which feeds the turbo inlet. That part after 30+ years usually falls apart if you look at it wrong.

I Think you are right. Chances i have a vaacum leak is high. I Made only a visual check.

i hav
e a question for you: the big S hose (turbo inlet pipe) has 2 metal rings tight with a screw. The function of the metal rings is to seal the junctions of the S pipe. I did not find any other gasket. Metal rings alone are enough for sealing the junctions?

Thank you very much

That junction is garbage...I have no idea why the TID is two pieces. When I still had a stock car, I had to modify the TID to get it to stay together. I think I inserted a piece of thin wall pipe (PCV I think) to give the two rubber sections something to grab onto. Then tightened down two hose clamps and it was good.

Back in the day, Corksport made an aluminum welded TID. Good luck finding one now. On a stock/hybrid turbo, a new TID is the way to go.

First try and locate your leak with either of the two methods I mentioned.

I triple checked all the hoses i removed first time i took off the airbox filter and it idles still at 1400rpm when hot.

What i'm asking you is if it's normal that engine warms very very slowly that what should be (for reaching the normal temp gauge level i have to drive the car: if i warm the car still in my garage temperature dont reach the normal level - gauge at 1/3 - mine is a S5 it should stay in the middle . While when engine worked well it reached the correct temperature even if the car was fixed in a place). Can a vaacum leak can cause this behavior?

And what about thermowax and air flowing sensor? Can these elements cause a high idle?

Think you very much.

Another detail i want to share with you is: when hot, idle stays almost always at 1400rpm but sometimes when i push the throttle and it goes back or if turn the car off and on, it lowers to 1000/1100rpm. Then if i throttle again it returns to 1400rpm.

Do you think this behaviour is also related to a vaacum leak?

I deep checked the TID (Turbo Inlect Duct) but the upper part and i didn't find any defect but i could not check or remove the part of the Turbo inlect duct that is connected directly to the compressor. Can i remove the lower part of the TID without removing any other part or is it needed to disassemble other things for reaching the bottom TID?

Thank you very much

Anyone?

I have the confirm that my car is "heavily UNDER-heating". Yes you read well: it's underheating, engine temperature doesn't go over 70 celsius.

I searched underheating in this forum and i found the post of this user:
https://www.rx7club.com/2nd-generati...oblems-104255/
Exactly my symptoms!!! Regarding idle if i drive fast it lowers from 1400 to 1200-1100rpm and the temperature gauge go up but never stays in the middle (a little under the middle - mine is a S5).

My theory (tell me if i was wrong) is that the engine doesn't reach the correct working temperature so the thermowax doesn't fully release and so the fast idle cam is not released. Can this theory be true?

So how can i fix this?

Thank you very much.