I have just fitted an auto throttle body and TPS to my car which is running a PNP90-93 and made the mods as DIY instruct. I powered up the PNP and hey presto the TPS gauge in magatune now moves in a nice linear fashion when pushing and releasing the throttle. So I do the TPS setup described in the 94 manual and everything looks good.... So far.

When I start the car idle immediately jumps to 2K and I get a really loud high pitched squeal / whistle coming from the engine bay - WTF? The squeal (scream) doesn't sound like terminal bearing or turbo failure so I experiment a little and when I blip the throttle it goes away and comes back as it moves back down torwards it's 2K idle... A short ride confirms that it is loudest at idle and disappears during a blip and or when moving along with the throttle open beyond a certain point. I have stuck my head in the bay and tried to identify where it's coming from but it's so fu&%ing loud and fades in and out seemingly all over the place.

Pulling the ISC valve connecter increases the revs (the idle screw is right in) and nothing I do in Megatune seems to make the blindest difference (even pulling the fuel right down in the zones it was hammering away in). Running with the pipe off the throttle body makes no difference either.

I have just sat down to take an Asprin as the thing has given me a right old headache.... Is this configuration or mechanical... I am lost.

 

IAC motor?

 

Agreed- I'd start by swapping your known-good IAC assembly from the old TB to the new one.

 

Alas this is the known good IAC from the old one... I took it off and cleaned it up and reused it becuase I didn't get another one with the auto throttle body.... Can they go bad that easily?? They are $150 second hand over here.... (UK)

 

Try opening the throttle screw some, its possible the iac cant control the idle now and gets stuck wide open, thus the high revs. IAC valves like to operate somewhere in the mid opening area (1/4-1/3 open) and if slammed shut or wide open, its out of its range. Driving the car may settle it down as well.


HTH Ron

 

Does the squeal go away if the IAC is unplugged?

 

Nope the squeal stays but the idle goes up to 3K... I got something at lunchtime to try and help locate where it's coming from (OK its a cardboad poster tube - but it should work) and I'll try it this evening when I get in..

I cleaned all of the IAC yesterday and the valve was moving freely. I guess air has got to be getting in somehow so I'll check for leaks tonight as well.

 

Progress?

 

Well after some investigation, I decided that I MUST have an air leak behind or around the throttle. This would give the high idle and maybe explain the noise symptoms. When the butterfly is shut the air is finding an alternative entry point and on the way in is making the godawfull noise... As the throttle opens, the air starts to go through the butterfly so takes over from the leak source.. So, armed with my trusy cardboard tube and some throttle clearner to spray, I rummaged around and found that if I sprayed on the side of the throttle the noise eased and the idle dropped some. I wiggled my finger down the side and could even play a a bit of a tune by tapping.

So I have ordered new gaskets for behind and below the throttle body and will take it off again at the weekend. It's a right bastard in traffic having a loud exhaust, a 2.5K idle and a high pitched squeak shrieking out... It certainly gets you noticed.....

 

Problem solved - I took of the TB and carefully cleaned both surfaces and fitted new gaskets between the TB to IAC and TB to Intake using a little silicone where needed. It started and now doesn't sound like a dentist's drill being amplified 5 times over.

I still need to play with the IAC settings in Megatune as with PWM idle set to "closed loop only" it's at 2Krpm but set to "warm up only" it's a nice steady 960rpm.

How do you make sure that what you set in Megatune for minimum and closed dc match the physical attributes of the valve? Is it trial and error or is there a scientific way?

Ta.

 

Best way is to use the values DIYautotune uses. They've done the testing already. If that doesn't work out, trial and error will be the best way to go about getting it to work right.