Toyota Repair: 98 toyota 4runner High Idle, cold air intake, loud muffler

Question
Hello Ted,

Bought the used 98 5sp manual w/cruise 6cyl with 129k.  The kid I purchaced it from had some shady looking air filter and had a loud muffler.  It had a slightly high idle (1200-1500 rpm).  (I know – BAD signs)  Gas mileage 17mpg - I think this is low for this model.  After purchasing, noticed the check engine light go on and off intermittently.  I Installed KN cold air intake.  Idle increased. (1500-2000 rpm) Cleaned throttle body.  Cleaned MAF sensor. Tightened air hoses. Light went off.  Idle still high.  Light came back on soon after.  Checked MAF – clean.  Cruise control - once was ok, now does not work.  When the engine is warm and I come off of the highway, the idle drops down to 800rpm and immediately bounces back to 2k rpm, and repeats; after 2 or 5 times settles back at 2000rpm.  Took into Toyota.  They said engine code said misfiring and that my plugs were of the wrong type.  I noticed that this engine requires plugs with 2 diodes so thought that might not be a big load of baloney.  I also though this could explain why I had more carbon build up and bad gas mileage.  They also said that the throttle body was dirty and that was why the idle was high.  I thought maybe true, since all I did to clean the TB was move the big valve flap and spray and clean it out.  So they changed plugs and cleaned the TB.  Guess what, still high idle.  They said that they noticed a screw which was moved from the factory setting (originally painted now moved) on the TB which can affect idle speed.  Evidently no spec exists for this screw.  They said I could play with it but who knows when I would get it right through temp variation.  Now I could have done the plugs myself for 15 bucks but I wanted to take the truck back after they fixed the issue.  They said they checked out things in front and behind of it and that I need a new throttle body. ($1000).  I can't find a used one for the 5spd and cruise (already bought one and brought it in to them and they said it was the wrong one).  They didn't mention anything about the IACV and said I needed the new TB.  Is this crazy, lazy or possibly true?  I am probably going to bring it another shop to get another opinion.  I know other sensors are involved, and not sure I am confident that they have found root cause.  I found a new TB on the web (Toyota part) for about $650.  I don’t want to buy the part and then find out it is something else that is wrong.  They claimed they are confident this is the issue, but this screw you can’t adjust seems a bit strange to me.  Can you shed some light on this please?

Also, the previous owner said that the clutch and timing belt were replaced when he purchased it at 90k.  I replaced my timing chain in my 85 (22re) but don’t know about timing belts.  Toyota charges $140 to look at it and who knows how much more to replace it.  I took a look at it (partially removed the cover) and it looked good.  Toyota said that if had not been replaced, it would have probably already broken.  Nice.  I did not see any cracks, etc but was wondering what indications I would have seen if it was going bad…  Just normal belt wear?  I know what that looks like.

Thank you very much.


Answer
My answer is going to be kind of short but to the point, I don't see any reason to replace the entire throttle body,I have never had to replace one for this reason, what I would recommend is to replace the idle air control valve, they are known to cause these kind of problems. That adjustment screw you mentioned is set at the factory and is not to be adjusted or tampered with, that's why the put the yellow paint on it. The timing belt is due to be replaced at 90K miles, if it looks good with no cracks on it it has probably been replaced already. Timing belts will last a lot longer than 90k but it's recommended at that time to prevent a breakdown, I personally have never seen one break. Let me know if I can clarify any other issues regarding this.