'92 civic vx w/ intermittent check engine light
 

So, I bought a '92 VX with 230k miles nearing 2010 in Dec. Car had the infamous idle issue; especially when using the A/C at all and then cutting it off. I live in metro-Atl; and emissions were failing initially, so took it to a a solid "Honda/Acura only" mechanic and had him pull the codes. One of which was the TPS. More on that in a second. He cleared those codes, but since I've had problems intermittently.

Here's what I've done to the car since:

Fuel filter was replaced right away and I slapped in a K&N drop-in filter for the heck of it to boot.

At the time, the car needed new plugs(NGK of course), wires(original Honda as all part store's OEM didn't fit right, I think its a Canadian model possibly, even though sold at a local Honda dealer originally)...

Anyways, after I got those replaced along with the distributor cap and rotor button, it finally passed emissions. My mechanic kindly cleaned the IACV for me as well.

I tried replacing the PCV valve prior to the cap/rotor button, but emissions actually got worse, *please see PS at end of post for a related question*

Also, I had to replace the CV joints. Cracked boots and cracking sounds. =P

Now, after those things the MPG went from 36/37 at initial buy to right around 40ish. I'm gradually changing over to a full synthetic(going to go 0w-30 Mobil1). I've used SeaFoam in the tank at my first oil change and put some in the crank case prior to the change for about 100 miles or so. I've got a syn-blend right now.

MPG has gone down some since needing to use the A/C with 90+ degrees lately, but I'm having an intermittent check engine light.

The light comes on while driving, sometimes its more susceptible while using any of the vent settings.

Primarily, though, its while coasting in any gear or at a certain speed for a measurable amount of time(more than just 2 or 3 seconds, but anything over 5 qualifies). Light does not come on during acceleration, but if anything while trying to implement downshifting for breaking. Not skipping more than 1 gear, if that, mind you.

I also have a 'jerking' to the engine if I try to keep the speed steady from time to time, usually while on the highway trying to maintain a speed like 50-55. It wants more gas if I try to maintain. Is that the lean burning aspect tricking me here?

TPS guys? This is my first thought since it was one of the codes my mechanic pulled. Honda quoted me to replace throttle body and TPS for over $600. Is there something that can be done to check this?

Thanks in advance.

PS:

I replaced the PCV valve with one from AutoZone, but I'd read reprots about the VX model not needing the 'slider' inside? I have the replacement on now and it has the sliding mechanism. This is the first manual car that I've owned for the record, but I don't believe it has anything to do with how I'm driving it.

Found out that my VX is definitely a Canadian model.

Possibly helpful information guys. Found the codes that were pulled by my mechanic, TPS may be one of them but on the paper they gave me these were listed:

Code #17 Speed Sensor
Code #22 VTEC
Code #48 LAF Sensor

These codes were pulled and cleared prior to passing emissions back when I first got the car.

I've checked my EGR valve for play then and it took a very 'moderate' urging to move, but I didn't have to strain or exert much effort.

My pops says I shouldn't coast in 5th gear, even though I'm doing 45-55 local roads. Its usually in the higher gears while coasting when the light comes on. It seems to always happen in 3rd gear or higher. I'm still a bit concerned about the aftermarket PCV valve from A-zone without reading up more on it.

coasting in 5th is fine. i'm a new honda guy myself. just be patient and the honda gurus will answer.

i'd expect to hear from TomO and Erik soon. they're great guys w/ a wealth of knowledge! there are more out there, i just know these 2 are still very active here.

It's not coasting if you're in 5th, it's engine braking (not very much "braking", granted)...but whatever you want to call it it's harmless and a legitimate strategy.

I'm definitely a newb still at driving a manual. Learning the feel for entering lean mode is fun, that's for sure. It makes it feel sluggish in response, though. Like I need to apply more pressure to the pedal to get an easily noticeable response. Its almost as though my low end torque isn't what it could be. Granted,this car probably needs a valve job or at the very least a valve clearance check.

My friend recently did his 2nd valve job on a fit(not the same car twice) and he's volunteered to do the valves on this VX.

If you have not replaced the O2 sensor, that would be the good place to start. I think the vx needs the O2 sensor changed more often than most cars to run right.

Okay, as an experiment I've gone back to the PCV valve that was on the car when I purchased it last December.

I reviewed my records and on the 2nd emisions test attempt, this AFTER the Autozone PCV valve was installed, the HC emisions were worse. Still the reason for the failure, but worse.

Also, when I pulled the PCV valve just now there was oil on the underside where the metal cylinder was supposed to slide. My theory is, if its a low pressure PCV system it may be causing a problem with the replacement part I had previously installed. I test drove it and no light, but I'll give it a week trial run.

On a specific note, the part Autozone said was 'for my car', it was a much harder fit into the slot onto the engine. The original was much more of a perfect match and it remains quite easy to pull back off of the engine block. If its a low-pressure system, this won't matter of course.

Update: Check engine light still happening while near 1500 RPMs. Mainly in 3rd or 5th gears, especially while trying to implement engine breaking. Probably because I push the RPMs a little higher while accelerating compared to downshifting. I also tried the 'maintain 1500 rpms while in 3rd', and it went off twice today when at full temp.

I'm going to take it to my mechanic to check the OBD1 codes.

...Unless, there is a way to verify on my own if its indeed the code 48 again? can I do the 'pins' trick to get the check engine light to flash the code myself?

I believe the LAF sensor is going or on the fritz. No idea if its original part or not. Thinking of investing in the NTK/NGK one if it is the problem. Fuel economy down to mid 30s on my last 5 gal fill with A/C on most of the time.

I agree that the LAF (oxygen) sensor would be a good place to start.

You should be able to pull the codes yourself.

Here's a link to the factory service manual- https://www.redpepperracing.com/technical/v/92Civic-FSM/

Here's the page with info on pulling the codes: https://www.redpepperracing.com/techn...0/aav.png.html

Sounds like it is the sensor. I kinda hope it is so I can just get the NTK/NGK replacement and be finished. Will try to pull the codes tomorrow.

Anyone know if the L2H2 helps/hurts FE compared to the L1H1 original LAF sensor? Or is the OEM NTK/NGK part the same?

https://www.oxygensensor.net/ntk_o2/24300.php