Idle issue

[Gitbox]

I recently had my throttle bodies off and cleaned the gunk from the butterflies. After assembling, I did the unauthorized TBS and found that closing the idle air screws did not lower the idle enough to have to bump up the idle stop screw. Odd, I thought. The sync went fine, but on the test ride I felt a very slight surging at normal highway speed like someone was pressing on the rear brake slightly and intermittently. Never felt that before. Power and acceleration are fine. It almost seems like an intake air leak but everything is nice and tight. Vacuum lines are all good too. No codes or problems in DIAG mode either.

Any ideas?

 

[Fred W]

The sensation you are describing is called lean surge.

It is probably due to a vacuum (air) leak somewhere after the throttle plates. Are you 100% certain that the engine side rubber boots were fully engaged before tightening the clamps? I found them a bit of a PITA to get fully engaged when I did mine on my '05

It may be that when you cleaned all the **** out of your TBs, now the worn holes around the worn butterfly shafts will leak more air. How many miles on your '04?

 

[Gitbox]

Thanks for the reply.

Only 32K miles on it. The boots have a groove in them that kind of snaps the rack into place. I lubed the rubber a little with silicone so they went in very smoothly, plus I did a visual and feel check the best I could.

I pulled the PCIII to test if that has anything to do with it. I might try the propane leak test. I wish these things had OBD II connectors.

 

[RaYzerman19]

Agree with Fred it seems like an air leak, but you also titled this an idle problem.... at what RPM range are you seeing the surge? I'd also agree you should double check the boots, even though it seems you did everything OK. If the boots have a 'groove' makes me wonder if they'd leak there if not snug or back in the same spot or if maybe the boots hardened up with age......

After that, I'd check that whatever you chose as the reference screw for the TBS (usually #3), recheck that screw is backed out at least 3/4 turn to 1 turn. Then redo your TBS. That said, I would think that should have less effect as RPM increases beyond idle speeds. Did you happen to remove the air screws, clean them and flush out the ports?

Can't speak for a Gen 1 lean surge, but the '06 & '07's had it in the ~3000 rpm range, that's why we put on PCIII's or PCV's. I'd recheck for air leaks before messing with your map, and if none, then maybe a slight adjustment to your map at some point. I mean, you've got it all cleaned up now, and things may have changed slightly.

 

[Fred W]

Ray, yeah my '05 also had the lean surge in about the same rpm range from day one, also cured by PCIII tuning.

Since the OP has a PCIII also, I'm curious what fuel map you are running on it? I had to get hold of a custom dyno map for my '05 to fully get rid of it. I have that map hosted here, if you want to try it: Custom PC3 Map for stock 1st Gen FJR. You will lose about 1-2 mpg as compared to stock fueling, but it is muuuuch smoother.

 

[Gitbox]

Thanks again guys.

I titled it "Idle issue" because I thought that bottoming all the mixture screws was supposed to kill the engine. It idled slower but not enough to stall the engine. Maybe that was a non issue.

I did remove and clean the mixture screws and seats with carb cleaner and they are all at almost exactly the same setting after syncing. In fact, the sync holds steady all the way up to 4000 RPM. I would think a leak in one or more of the boots would make one or more of the mixture screws noticeably different than the others, that is unless they all have exactly the same leak. I even tried looking for a leak with propane and found nothing. The surging is around 3000 RPM. I rode it after removing the PC III and cleaning a corroded connector pin as mentioned in another thread about this same issue and the surging is now almost imperceptible.

There is another factor here I did not mention and it may be relevant. I had the final drive gear ratio changed so that it now lowers the engine RPM by 10%. That puts the it closer to the 3000 RPM mark with my normal driving, therefore I may have had a little of this well known lean surge all along but just did not notice it.

I'll drive it around some more and when I reconnect the PC III, I'll try Fred's map and see what that does.