Occasional Fluctuating Idle (700-2000 RPM) While @ Stops "rrrrRRRRrrrrRRRRrrrrRRRRrrrrRRRRrrrrRRRR"

Subjects:
-Throttle Cable
-Setting Base Idle Speed
-Brake Booster

For JimBlake (and others):

Seeking to get my idle issue resolved, based on comments and research I find the need to follow the instructions on the post "Setting Base Idle Speed" before messing around with the brake booster, right? However, one thing mentioned in that post is to not adjust the throttle cable, which is something I made tight a year ago and it's the only reason I now have 700 rpm idle instead of 80, so I am curious on how to get it back to its original position - how would I know what its original position would be? 80 rpm? I'm thinking I need to do this before proceeding with resetting the base idle so that I can then mess around with the brake booster. Is this logical?

 

0 rpm. The throttle cable shouldn't hold the throttle open at all at idle. The FSM shows that the cable should be adjusted so there's 10mm to 12mm deflection in the cable between the throttle body and the cable bracket i.e., the cable should be slightly loose when the pedal isn't being pushed.

 

Get the proper slack in the cable. Clean the tb - both sides of the butterfly and the two ports that go to the IAC and FITV. Next, clean the IAC, only happens when the car is warm. Be sure the coolant is full and there is no air in the system, this can "mess" with the IAC and give it false readings.

The brake booster pulls extra vac on the engine, as long as the system is sealed - no hose or booster diaphragm issues - the IAC adjusts for this extra "load".

 

this is exactly correct!i will not add to this reply i have a honda repair manual an it says exactly what Roader said!good job Roader

 

Thanks for your responses. Right after I posted this thread, I knew I wasn't going to be patient for a response and went ahead messing around with it.

Doing the following while the engine was running to see what would happen to the idle, and while having the air-intake separated (this wouldn't do anything as the throttle panel was in idle and would keep air out anyway), I first:
* Unplugged two circuit plugs, one on either side of the PGM-FI, one at a time, by themselves separately and then together; I was thinking they were the IAC and the FITV.....NO CHANGES IN THE IDLE
* I then noticed a third plug that connects to the front of the PGM-FI (I'm guessing this has to do with PCV or the Exhaust Return); I unplugged this and immediately the idle dropped to less than 100 RPM. If the car didn't die at this point, as it sometimes did, it would hold this RPM steady. Disconnecting this cord with the others or by itself has the same result - plummeting revolution per minute. Therefore, if the first two cords are IAC and FITV, disconnecting them doesn't seem to have any immediate consequences.
* Lastly, with the third plug unplugged, I open up the vacuum tube that connects with another in front of the brake booster. This allowed the engine to rev and hold steady a bit above 2000. Interestingly, with all electric circuits plugged and opening this tube had the car fluctuate in it's idle, but unplug that third plug and it revs.

It was at this point - though I did experiment with the cords again, trying all variations to see what would happened: nothing different from what was already mentioned - I discovered what you all have stated: the throttle cable doesn't have anything to do with the idle. I messed with this later.

I proceeded to then mess around with the ECU. All variations - unplugged, plugged, unconnected, connected....made no difference. Simply removing the ECU fuse at any of these junctions killed the car every time.

DON'T DO THIS! Remove the ECU and then quickly put it back it, which allows the car to 'save' itself while dying out. (I think this puts in a "false" value that it runs the car on)

After I did this and turned the car off, it didn't want to start like it normally does, and when it did, giving any gas of any amount of pressure on the pedal had no effect - the engine simple refused to rev! In fact, giving it gas seemed to "drown" it, making the engine 'sigh', almost. Fortunately, turning the car off, removing the ECU and disconnecting the battery and letting it sit for a few minutes while I went back to putting back all the tubes, wires, and air-intake back in their proper place was all that it needed so that when I put the ECU fuse back in and started the car, it came to life like it always does. Not only that, it now idles a bit above 700 (probably 720 ) and since that day, I have not noticed the fluctuating idle at stops like I sometimes do. However, when I brake hard, it does spike about 50 rpms and then drop 100 rpms (50 rpms below initial rpm before spike; that is, +/- 50) before returning to the 720, but overall, I think the idle has been fixed. THANKS TO THIS FORUM!

With the idle where it seemed it was suppose to be - based on what I've read in this forum, I therefore set it just to the point that the slightest touch of the pedal revs it another 50 RPMs or so.

 

Here's a picture for 1991 car to go along with the post about setting base idle.

#15 is the IACV - unplug that and the idle drops low??

#8 is the fast-idle valve (FITV); MAYBE take off the cover & clean or tighten it. Search for a post about tightening the FITV.

#9 is the boost valve. I never had an older Accord with one of these valves, so I bet Poorman will know better then me what that does & how to clean/adjust it.

 

Thanks Jim. Long story short - I fixed the idle. I generally followed the steps listed in the post "Setting Base Idle Speed".