idle hunting story
 

What's up gurus,

Help me diagnose this issue. I'v been having an idle hunting issue for a while when the car is in park and in neutral. When I put it back into gear it idle almost fine.
I received no engine codes. I replaced the Maf, O2, Map, spark plugs and ignition coils and they did not solve the issue. I know its not the tune.
So 2 and change years ago when I started my Rotrex supcharger project I bought a used throttle body from the junk yard and its been knocking about in the garage.
I decided to clean it up and swap it with my existing one. Low and behold when I started the car, my idle was purring again. Problem solved!!!!!

The car drove normal until just now. I did a few WOT's to test my new 85mm pulley out that would give me max of 13psi with the AEM water/meth kit that I installed. The car pulled well and ran 10.1-11.1, so I know I need to tune some more.

Here is the issue, as I came home and put the car in park, the same Idle hunting started again. I am so dissapointed.

Did I screw up the IAC in the other throttle body? What could have caused that? Or was the other one on its way out being that I did pick it up from the junk yard from another 97 E320? I am reluctant to buy a new one and worried that the same thing will happen to that one. Please advise if it is possible that the second one was on its way out and what should my diagnostic be? What is the recommended torque for the throttle body bolts? Possibly not torqued properly and the pressure is causing air to bleed out from the seal?

Oh boy the questions I have. I need some direction here....plz.

Rock

I would check for vacuum leaks. See if any hoses came loose or vacuum lines.
There are just so many things it could be but a vacuum leak would cause some issues for sure and if you are running 13psi that could certainly do it.

Your right. That should have been the first thing I did. I hope it is. I'll check tomorrow.

On another note, right now I'm running 100% distilled water to cool the air down. Should I use 50/50 mix or straight M1?

thats a nice motor

Thank you.
Here's a photo of the meth tank in the trunk

wow,cool setup.I lost all interest in racing,and cars after my daughters passing in January.At one time,I wanted to force induction my m104.

Found 2 vacuum leaks. Fixed them and idle hunting still persists.

The wiring on the TB's (IIRC) were bad as was the rest of the wiring on these era cars. You can pop the side off the TB and see the wires enter and if they're in good shape or not.

Look at the pictures. What do u think? Click on the link please.

Sorry fastest way to show multiple pics right now.

Test - MBWorld.org Forums

Situation got worse. On cold start the car bucks and shakes and throw all kinds of codes. 02 , misfires and map sensor circuit codes. I already threw money on most of the parts in the past month(maf, map, plugs, coils and O2)
So after I drive the car a few miles, it starts not doing all of the above but goes back to my original idle hunting issue.
Battery at 12.5v with car off and 13.5-13.8v car on.
Also wiggled around the harness to the throttle and to the ignition system and stil idle hunts.

Reset the ecu. Turns on and stable until close loop kicks in.
Changed the coolant temp sensor. No different.
Just ordered new O2 and will change back to original throttle body now.

Does this sound right?
I did a smoke test through one of the vacuum hoses. I also plugged the intake to the supercharger. The only place smoke was exiting the engine was through the valve cover breather holes.
Can I eliminate vacuum leak now?

Shoot, I was hoping the smoke was coming out of the intake manifold gasket or something. Darn.

Solved!!!!!
 

Bad AEM Fic. Bypassed the fic and the car runs fine on factory ecu. I can drive but l have to baby it under 2700 rpms and low load. Sometimes it's just darn easier to diagnose the free stuff instead of throwing money at it.
New fic arriving today I will extend the harness and install it in the glove box. This way it's not exposed to the NY environment and the heat from the exhaust.
Thanks for all your help. Much appreciated fellas.

Re-solved
 

Just to let u guys know the new AEM fix did not resolve the idle issue however, I relocated it into the glove compartment. Apparently me messing with the harness to the AEM caused the corroded pins to go bad. I replaced the AEM with a new one and the idle hunting continued.

The issue was solved when I installed another used throttle body again. My factory one went bad. I installed another and idle was fixed. Then I started boosting hard and the idle was hunting again. I bought another TB from a junk yard in California which was in better condition than my factory one. This one did the trick. I did not boost the car for about 75-100 miles. I figure the ecu needed to adapt. I just started boosting again and the idle is smooth as factory all the time even during warm ups. I'm just reluctant to boost really hard now as I'm afraid this throttle body can go too.

I figured theses throttle bodies are about 18 years of age and the potentiometers gets worn out after hard WOTs. I paid $120 for the TB which is not bad. If this happens again, I see online has them brand new from $1000 to $1300. Guess that will be my next option.

Closed(for now)

Thanks
Rock