'93 DeVille What is the Proper Induction Cleaning Procedure

[Rob Bruining CLC 12428]

My '93 4.9L idles a little rough. It has newer plugs and wires. I've cleaned the throttle body with a cleaner using a toothbrush. I've added Lucas to the gas and run a cleaning procedure with Sea Foam through a vacuum line. Do I need to take off the idle motor and clean any passages? Is there something else I should do? The car has 134K. Thanks.  Rob

[CEC #20099]

I have a 90 SDV 4.5, 168K miles, which is the same basic engine. You need a shop manual so you can interrogate the computer for fault codes. Being OBD 1, you might not get much. Use the digital dash for this.
At that mileage, if the injectors have not been serviced at an injector shop, & if the EGR has not been replaced, you know where to start. I would suggest a compression test, but the access is impossible. Please furnish more detail, if you can.
My local Cad dealer charged $125, for the first hour of diagnosis, last yr. I do virtually all my own work.
I have not had to clean my induction system.

c chleboun #20099

[TJ Hopland]

Does it have a check engine light?  If it does you can get the codes from the climate control system.

How does it start and hows the mpg?   I have seen a lot of these with failed fuel pressure regulators.   This causes hard starts and poor mpg.  The regulator is attached to the fuel rail but not part of it like some models.

Is the base timing correct?  Have seem more than one time on these motors where the distributor got loose and drifted out of time.  When the base timing is not correct the computer tends to hunt for its happy place which it usually wont find if the base is wrong.   Same can happen if the throttle has a stop screw (dont remember if that one does).   The IAC is supposed to control idle speed but if the throttle is not closing again computer hunts for the happy spot.