cleanint of TB and idle RPM?

[Dinkydow]

I just noticed my 94Q is idling at 1100 RPM warmed up, without air on, in neutral. Iam sure it used to idle at 750. I did clean the TB a couple of weeks ago. Could this be a the reason? Will the rpm's go back by themselve or do I have to change it? If so how?? Thanks Wayne

[forecast]

The normal idle is 650. Your's is what you might expect from an IAC valve stuck wide open, which it may well have been before the TB cleaning.

Ideally a brand spanking new clean TB should let just a bit less then enough air around it for 650 rpm. The computer opens the IAC a % of time to move the Idle up to 650. The IAC should only be on 20% duty cycle (at most).

Squeezing off the IAC line should cause just a tad of idle dropping. If your IAC is too hard to squeeze then don't break it!

If you squeeze off the IAC supply line (runs parallel under the air duct to the TB) and the Idle drops significantly then disconnect the IAC control wire. If the idle is still fast (and you could reduce it by closing the IAC line) then the IAC is stuck open.

I'm wondering two things - did you get all the hoses back together tight, and did any vac hose crack during the TB cleaning operation?

Dan

[Dinkydow]

Dan, Thank you very much for answering my question and also for the info. I really do appreciate it!! Wayne

[Q45tech]

The manual bypass screw [on IAC] is how you set idle speed.Prior to ecu intervention.It should be in a narrow range of 2.5 to 3.5 turns out from being bottomed out [turned all the way in]. if the TB is set correctly and everything is clean........this gives the ecu maximal trim range to maintain the idle at 675 rpm with varing loads from alternator, power steering, ac compressor.

Warning you must make sure the coolant temperature as read by ecu is more than 171F but less than 194F [ideally 176F] when setting the manual air bypass!

Since much of time is at idle in city any excess rpm [above that needed for smoth idle] affects gas mileage adversely.

[Dinkydow]

Thanks Q45Tech, I appreciate your help. Iam just a guy who loves his car, not much of an expert on working on it. I wouldn't really know when the temp is between 171 and 194f would there be any rule of thumb i.e. have had it run for 5 minutes before I adjust it??? Thanks Wayne

[juiceman]

Go to your local supermarket and buy a cooking thermometer

Open the radiator cap and stick in the thermometer

I think it is ok to run this way because the pressureized system just increases the temp that the water will boil at

When done just recap the radiator

Q45 does the turns you mention on the IAC apply to the J30 Also?

[Dinkydow]

Thanks Juiceman, sounds good to me. I have a cooking thermometer so I will give it a shot. Thanks for help!! Wayne

[maxnix]

Calibrate any thermometer to the boiling point of distilled water, adjusted for barometric pressure.

[Q45tech]

Let the car idle for at least 10 minutes or 3-4 minutes after the inside gauge is normal 3 o'clock........no headlights , heater or AC turn everything off because the ecu reads the voltage and can trim the speed..........you can't trust the inside tach to be accurate enough ...........why the Consult is used ..........but 700 is better than 950 for sure!

If the engine shakes at what you think is 650-675 means some injectors plugs are dirty and the idle is not balanced!

[Q451990]

Open the radiator cap and stick in the thermometer

Sounds like a good way to get burnt and make one heck of a mess!

Heath

[PalmerWMD]

Open the radiator cap and stick in the thermometer

Be sure to open it <before> the system is hot + pressurized.

Fred...

[juiceman]

yeah sorry I just assumed that that was a given

[Dinkydow]

Thanks everyone for info!! I should have the info I need , I really appreciate getting this help. Wayne