Driveability Improvement: Secondary throttle plate adj and O2 sensor repl
 

I had been having minor problems with touchy throttle response and occasional hesitation/bucking during mild acceleration. I narrowed it down to three possibilities:

1. Sticking secondary throttle plates
2. O2 sensor on its way out
3. TPS out of adjustment.

Over the weekend, I finally got around to doing something about these issues.

Secondary throttle plate adjustment
First, I moved the secondary throttle plates by rotating their exposed linkage. The plates were noticeably sticky coming off the closed position. I first removed the elbow and cleaned the bores (which were not very dirty) around these plates. This did not remove the stickiness. I then adjusted the secondary stop screw 1/6 of a turn tighter. This totally removed the sticking. On startup, the idle was now a bit too high, around 900 RPM. I adjusted this back down to ~750 RPM with the air bleed screw on the bottom of the throttle body.

In driving the car, throttle response was now much more smooth and linear, and matching RPM’s during shifts while driving sedately was also MUCH easier to do. However, the hesitation/bucking I mentioned above was not totally eliminated, although it was not nearly as severe as it had been.

O2 sensor replacement
I then installed a new generic Bosch O2 sensor ($18 – Bosch # 11027). After this, the idle speed again increased to ~900 RPM (indicating to me that the idle was now significantly leaner than it had been – apparently the original O2 sensor WAS on its way out, causing the idle to be too rich). I again adjusted the air bleed screw to bring the idle back to ~750 RPM.

In driving the car, ALL of the hesitation/bucking is now gone! I did not check out the TPS, since it now seems that it is properly adjusted.

It will be interesting to see if these changes improve my around-town gas mileage from its recent 15-16 mpg.

Good info Dave. How many miles on your car?

Cool!!!

I wonder if that will cure my 3K hesitation. I will try to replace my O2 sensor...

Thank you...

Nope.

~57K miles

my car does soemthing similar. on/off throttle feels really sloppy. also on very very lite throttle (just enough to maintain speed) i get some break up. i was thinking its the tune. but people have also recommended changing the o2 sensor. here is the question....if the power fc is set to not take the readings from the o2 would replacing the o2 not make a difference? i know the question seems silly but 1) perhaps the ecu still uses the 02 to some degree even though its turned off and 2) who the hell knows with these cars..lol.
another tid bit of info....even when i am in neutral and hold the throttle to maintain say 3k rpms it will break up a bit. the car accelrated perfectly clean and i have played with the fuel by removing and adding to pim volt however the problem doesnt get any worse or any better. i am at a loss. of course i dont have a wideband so it makes it that much more difficult.
anyway your help would be much aprreciated as this gets pretty annoying when cruising around town.
tks

Sorry. I would like to help, but anything I would tell you would be BS, since I have no experience with a power FC.

Dave

Chuck Westbrook

After seeing this thread I went out and bought the new oxygen sensor. My car drives better as well. On/Off throttle response is better.

The biggest difference is my idle. Its now smoother. Also, my exhaust used to smell horrible and literally burnt my eyes! Now, it smells fairly normal (as much as a rotary can) and doesn't burn my eyes! Woohoo!

:) Great! That's why I posted this - to maybe help someone with similar problems!

I noticed the improved idle smoothness (it wasn't missing before, but the combustion pulses were more peaky, causing a bit more vibration), too, along with its seeming to be a less loud at idle, but I forgot to mention it.

Dave

Thanks Dave,

I think I'll replace mine too. It must be the original, and at 62K, its time to get a new one. I hope it helps my gas mileage. 9 mpg in the city :(

Well, I don't think it'll double (my 15-16-mpg "around town" driving includes quite a bit of freeway), but I'd bet it'll probably improve at least a few MPG.

I didn't really know that anything was wrong with my O2 sensor (I'd just passed emissions testing 2 months ago with flying colors), but for only $18, it sure was worth trying. That it had such a noticeable effect was a bit of a surprise.

Dave

For only $18, would it be worth it to change the O2 sensor on a more regular maintenance schedule, say maybe as often as you change the spark plugs?...

Naw. The O2 should last for a lot longer then the spark plugs. ;) You should be able to get about 25-30k miles on the O2 before it's burnt up. I would put an O2 change on a similar schedule as the fuel filter.

OK. A question: Have you had this experience - O2 sensor change making that big of a difference?

Dave

Nope, not in my changes but I never experienced the problems you mentioned in your original post. When my O2 was bad, I never had any hesitation or anything. To be honest, I didn't notice anything different from when it was throwing a cell to after I replaced it. ;)

Well, that's what's odd about my situation - that it could be bad enough to cause driveability problems, but not show any other distinct symptoms or a CEL.

Dave

When I was still running the stock ECU, replacing the O2 sensor made a significant difference on my car. Mine had bucking problems, not so much hesitation, which were greatly improved by replacing the sensor. The idle was much smoother as well.

Another thing that made a big difference on mine was adjusting the dashpot. It was pretty worn out by the time I got the car, so I adjusted it a little farther out than the FSM specs, and that got rid of the remaining bucking when lifting off throttle at low speeds.

Now I run a PFC with O2 feedback turned off, so the O2 sensor is just a plug in the downpipe. That's what happens when you do a recalc on the base map and don't restore the idle region.

aaron1017 and DigDug, thanks for the confirmations.

I'm really glad I posted this thread - maybe more than a few people will make their FD's drive better because they saw this.

Dave

No problem. :icon_tup: It was worth the gamble for $21 dollars (from NAPA Autoparts) and 30 minutes to install (solder wires + shrink wrap and install into DP). My Oxygen Sensor Socket makes it easy!

http://www.toolfetch.com/media/44412.jpg

or

http://shoptoolsshoptools.com/images/4491c.jpg

Between adjusting my TPS, new o2 sensor, and adjusting all the setting on the throttle body... it feels like I have a totally new car as far as low-end, low speed, and light throttle applications go!

I had my o2 sensor go out on my Acura (OBD2) and not throw the check engine light. I got ~220 miles to a tank instead of the usual ~330!!!:shocking:

I know that this thread is old but replacing the o2 sensor on FD's is as easy as unplugging, unscrewing, replacing and re-plugging right?

very good thred.
i have same issues but no problems with sticky plates. I'm replacing my O2; plugs and wires soon so i hope for improvements, especialy in my single digit MPG :)

Yup. That's basically it!

Dave

cool im going to replace AT LEAST my o2 sensor this weekend!