Poor (still) FE on `92 VX

[4bfox]

Hi:

Well, I appreciate all the help and tips I've picked up here, have learned a lot about my VX. Still getting poor FE....around 34MPG on last tank. This is after swapping the engine/trans out for a new(er) version (old trans was dying), checking and cleaning all the solenoids (per TomOs inst), and adjusting idle.

Idle is still "bouncing" from 1K to 1.5K, then SOMETIMES it will idle @ 600rpm. I'm wondering if prior owner didn't "chip" the engine, and I just haven't found it yet....are there common locations I should check out? From what I've read, these are usually spliced into the wiring harness (usually to the ECU), right?

What about the ECU? Do these get flaky? I work on PCs every day, and int. problems are a ***** to troubleshoot, which looks like what I have here.

Any advise will be appreciated.

[mrmad]

If your idle is bouncing around, you could have a leak on the intake manifold somewhere. I would take a hard look at all the hoses and connections around the IM.

[GasSavers_Ryland]

I tried the next heavier weight oil, and my idle problem went away compleatly, this was of course after I replaced the gromet that the PCV hose goes in to that is below the intake manifold, it was so dry and shrivaled that it was not sealing at all, that helped a bit, but defently 10W 30 oil helped (had 0w30 befor), so check every hose, pull off each of the venting hoses and block them to see if that helps too.

[4bfox]

I appreciate what you're saying, but if it's a vacuum leak, wouldn't it bounce ALL the time? Like the other day, I drove about 32 highway miles and noticed when I coasted down a couple of long hills, it was bouncing (1-1.5K). Then on the way home an hour later, it was rock-solid at 600 rpm. I'll go through everything again, I may have missed something.....

[djenyc]

I have the same problem on my 94 Civic with bouncing idle, changing spark plugs, and cleaning IACV didn't help. Will probably do Oxygen sensor next, hopefully that will help.

Please keep us updated on what worked and didn't work in your case.

[4bfox]

Yeah, I've been wondering if the O2 sensor can cause this scenario....I'm about to the point of replacing mine, too. Will post my experiences...

[Danronian]

I would make sure your throttle body plate is clean and sealing 100%. If it's not sealing due to gunk/buildup, your car will not idle correctly. From what I've read, the engine should have the throttle body closed at idle, and if it isn't closing 100%, this could cause the issue.

I had a similar idle issue with my old VX motor. I swapped in a lower mile one with the same o2 sensor, and now the idle issue is gone.

I've heard of maybe one person being able to chip the VX ECU (which is done under the ECU cover), so the chances yours is chipped is very slim.

[Gary Palmer]

I had a similar issue on my 89 Honda. Try taking the hose from the IACV valve, to the intake, disconnect it from the intake and plug it off. If the idle steddys down, the IACV valve has something gone bad. On mine everything I checked seemed Ok, but apparently at a bad time juncture in the cosmos, some knicks or something caused the IACV valve to look Ok, operate Ok, but still not quite seal properly.

The symptom is caused by air leaking into the intake, causing the ecu, with the oxygen sensor to go hunting to try to get an A/F that is correct. Since it can't, within the range it is set to try for, it falls back and trys again. (This assesement is my own, based on finally figuring out what was causing the problem, on mine, after I had checked, cleaned, spanked and done everything I could to find the problem.) If you plug the hose from the air intake, with a bolt or something, the car will still idle and run, until you get a chance to get a replacement IACV to install.