93 Civic VX: Tuning up hesitation and rough idle

[GTR]

Hello all,

First off I want to thank everyone here for the wealth of great information! I just bought an unmolested VX with 228K last week and have been learning all I can about it, and the posts here have been a huge help.

When I got it, the radiator was cracked (overheated and blew all coolant out before I got 4 miles hah! putty to the rescue!) and it idled a bit rough around 800-900 rpm and had some dead spots and hesitations when accelerating, and had trouble delivering torque when at <1600 rpm at times.

So far I've replaced the radiator, spark plugs, spark plug wires, fuel filter, and cleaned the IACV.

The plugs and wires and fuel filter made a nice difference. I think it had original plug wires, they were nasty. I replaced with Denso 671-4183, for 30 bucks.


The spark plugs themselves were in good shape, but someone got lazy and had put ZFR5F plugs in it, which I replaced with ZFR4F.

That made a huge difference in the hesitation, and in the steady pull of the motor. Very happy. Idle seemed smoother as well.

Then I pulled off the IACV, and it was 80% blocked I'd guess. Lots of carbon dust on the filter. Sprayed it with brake cleaner and aired it out. Put it back on and WOW, huge difference!

The idle is completely different now. When cold it idles at around 1000-1200 now for a bit. It seems to stay there, unless I blip the gas, then it drops down very, very low. I thought it was going to die. At its lowest idle, the tach needle is between 0 and the first line. It seems to adjust it's idle up and down a LOT more now as well. Generally from around the first line up to about 7-800.

So I'm not sure about the idle. Clearly it's more efficient since it's often 50% less rpm than it was before. When it drops down to the lowest point, the car does a fair amount of shaking. At around 5-600 it seems to be pretty smooth.

Driving wise, it's much better than before. The previous owner said he got 45-52mpg city/highway for the last 16 years. We'll see what I get. MPGuino is on the way.

Do I need to reset the ECU or anything for the car to relearn some parameters since I changed so much?

Thanks everyone!

[Ecky]

Check the ignition timing. After that, adjust the idle screw with the ECU jumped until it's a little below where it's supposed to be, which for most Hondas is 750 +/- 50.

Congrats on the awesome car!

[379Kcivic]

Congrats on the VX!

My '95 had some of those same issues: cleaned the IACV and adjusted the idle so far & it runs pretty well. I'm sure that a tuneup/fuel filter would help, but with about 50/50 city/highway mix of driving I'm averaging 44 after almost 15K miles.

I'd bet a valve adjustment as well as new PCV/EGR valves would help as well. But at 279K & decent mpg I'm not complaining.

But I'd say the biggest improvement came from driving more conservatively and going back to the stock tire size.

I'm looking forward to hearing about other improvements in your VX.

[user removed]

Idle speed is low, less than 600 RPM. Mine was barely above the 500 RPM mark when I got the car with under 28k original miles in 2008. Clean out the EGR passageways if they have not been done, almost certainly needs that at that mileage. Low idle speed minimises fuel waste when idling and the EGR function helps keep it running smooth, especially in lean burn. Mine would accelerate smoothly from 30 MPH in 5th gear at 1000 RPM, even with the AC running.

regards
Mech

[PaleMelanesian]

Check your exhaust manifold. Mine had a crack at the O2 sensor and when it opened up enough my idle was all over the place. Stumbling at 300 rpm, then surging to 1800. Replacing the mani-cat fixed it.

[Ryland]

A common pattern for the hesitation is bad o2 sensor, unplug it to test it, if the problem goes away then it's the o2 sensor, while it's unplugged it's running in open loop mode and will be running a bit richer and will never go in to lean burn.
Other problem that can cause hesitation is a bad throttle position sensor, but that is much less common.

Common problem that causes idle bounce is a vacuum leak, check the PCV system including the lowest point in the hose, under the intake manifold, there is a grommet that drys out and shrinks causing a vacuum leak, $3 part and someone with small hands tends to take care of it.

[GTR]

Originally Posted by Ryland

A common pattern for the hesitation is bad o2 sensor, unplug it to test it, if the problem goes away then it's the o2 sensor, while it's unplugged it's running in open loop mode and will be running a bit richer and will never go in to lean burn.
Other problem that can cause hesitation is a bad throttle position sensor, but that is much less common.

Common problem that causes idle bounce is a vacuum leak, check the PCV system including the lowest point in the hose, under the intake manifold, there is a grommet that drys out and shrinks causing a vacuum leak, $3 part and someone with small hands tends to take care of it.

Well I unplugged the o2 sensor and voila, all hesitation ceased. Guess that's good news and bad news. At least I know what the problem is, bad news is the price.

What options are there for replacing the o2 sensor that don't involve buying the very expensive OEM part? Can they be cleaned or reconditioned much?

I see some on ebay for sale as well, how are those?

I also found this from searching, seems not too bad and it's an NTK.

www oxygensensor.net/ntk_o2/24300.php


Thanks for all the advice, very helpful everyone!

[SmellyCat]

Some times the o2 sensor needs a good cleaning. Carbon and crude

[slownugly]

Watch what sensor you buy. Cheap ones might say the same part number but they might not work correctly. The original number had lza09 etched into the sensor. Many aftermarkets will say lza06 lza07 lza08. I had the a08 in mine brand new and it had a terrible stumble. Replaced with an a09 and it was fixed. I believe It came in a denso box but had the ntk numbers on it. Or go straight to the dealer. Not cheap but a good gaurantee

[greasemonkee]

Originally Posted by Old Mechanic

Idle speed is low, less than 600 RPM. Mine was barely above the 500 RPM mark when I got the car with under 28k original miles in 2008. Clean out the EGR passageways if they have not been done, almost certainly needs that at that mileage. Low idle speed minimises fuel waste when idling and the EGR function helps keep it running smooth, especially in lean burn. Mine would accelerate smoothly from 30 MPH in 5th gear at 1000 RPM, even with the AC running.

regards
Mech

The presence of EGR gasses only seems to be for emissions in the way this engine operates. I've driven mine for the past 60k miles with no gasses actually flowing into the engine, but the ecu thought the valve was open so it was adding a load of extra timing. Once I fixed the EGR valve it lost considerable part throttle power probably due to timing, but otherwise there was no appreciable change. If it weren't for the ECU I'd throw the thing away.




I've found that the egr valve sensor needs to be greased/cleaned periodically.


Make sure the pcv line is open to the crankcase, the engine gets a good portion of its idle air through there. While setting the idle speed follow the Helms idle reset procedure.


A basic vacuum gauge is a great tool for running on the max threshold of leanburn with a quick glance - not sure if the mpguino has vacuum or not, but I'm sure you'll be able to see where leanburn activates.