I'm grateful for this site, and the helpful members here. I've used the search feature, and previously, compiled a list of suggestions that I printed and gave to my mechanic from various threads here.
My wife and I have a 1992 Civic VX hatchback, 5-speed, with 200,000 miles on it. We are the only owners, and it has always been kept stock, except for retrofitting the A/C with the current system. It's always been a dependable, honey of a car, and without the A/C running, I can easily get 46-50+mpg depending upon the types of miles driven each tank.
For the past couple of years, I've had a stumbling/hesitation problem that has gotten worse. Finally, a few weeks ago I brought it to a good local shop with an experienced Honda tech. We replaced the plugs (Nippondenso), cables, MAP sensor, coil (old one was cracked), ignitor, injectors, and ECU. Unfortunately, the hesitation problem remains.
The hesitation is worse when the engine is cold, and improves as things warm up. It never used to stumble when cold, and, interestingly, this problem mysteriously became slightly worse after replacing the ignitor. Replacing the ignitor cured a stalling issue that would occur at the same place 5 miles from our house, so I'm confident that the new part is good. As the engine warms, the problem becomes more of a subtle hunt/surge when driving a steady rate, or an abrupt "pause" when accelerating.
As you can see from the above, we've dumped a boatload of dough into repairs, and have little to show for it. Any ideas? The mechanic is stumped, and doesn't know where else to check. Fuel delivery is fine, and the engine barely cranks when the key is turned, before firing right up. I change the fuel filter every couple of years, but this is probably unnecessary given the car only gets driven ~3-4,000 miles per year.
I'm fairly certain he checked the vacuum, as one of the other employees mentioned that the way they check this is to pressurize the system with smoke and look for leaks.
One other thing of note. Initially, when he checked the MAP sensor, he got a reading that didn't jive with what his manual said it should be returning. So, he ordered a brand new one and installed it. However, the new MAP gave the same values that the old one did. Fortunately, since this was his error, I didn't get charged for the $300 part! But this has me wondering...perhaps is there something else causing this sensor to throw incorrect values? (I don't know what specifically these values were.)
The last things done were replacing the injectors (after cleaning the old ones failed to resolve symptoms from two of them), and the ECU. I have more low-end torque now than I remember, but the idle has dropped from a rock-steady 1500 previously (I was told years ago that this was due to a faulty idle air motor) to a stumbly 800-1000. After some reading, I learned that an OBID-I ECU doesn't require relearning, although I followed the same protocol when installing it as is recommended with an OBID-II
The only other part that hasn't been checked is the EGR valve, although I'm pretty sure the engine would be running much worse if this were clogged, and wouldn't improve as the engine warms. The hesitation seems pretty much confined to the 1500-3000RPM range.
And finally, this is totally off the wall, and I understand is a known issue with these older Civics. But I go through dash dimmers like crazy! I wonder if this might be a related symptom, somehow...
As you're finding, troubleshooting for a slight hesitation is one PIA. I would download a manual to help figure out how to:
1. Check the throttle position sensor
2. The engine coolant sensor (the one that feeds the ECU)
3. The EGR valve and system.
Though I agree the EGR should get worse when the engine warms up, it's real easy to see if the EGR system is clogged (pull vacuum on the hose feeding the EGR at idle and it should kill the engine).
It probably wouldn't hurt to clean the engine grounds. It might not hurt to check your O2 sensor, but I don't think this is it since when the engine is cold, the car should be running in open loop and not using the O2 sensor.
It was about fifteen years ago, I believe, and I had brought the car to a shop for some other issue. The mechanic was trying to keep the repair affordable, and didn't replace or clean the IAC, but suggested that that was behind the rough idle. He may have sped up the idle to smooth it out, and it never concerned me beyond that point, since the car otherwise ran beautifully -- plus it was nice to have a smooth idle, albeit a fast one. This model Civic is geared very high, and a faster idle made accelerating from a stop more predictable. (I've driven manual transmissions for 35 years.)
Does the IAC affect other modes of operation, beyond idle? I thought once the RPMs lifted beyond what the idle was set for, the IAC was disengaged. I looked up how to clean it on Honda-Tech.com, but noted that all the symptoms (which, I agree, may be present with my car) only have to do with idle.
I tried Googling cleaning the throttle body, and couldn't find any good guides. I have had offered a "super-cleaning" service by a couple shops, where they hook up brake cleaner to the intake and let the car run for an hour or so. This sounds drastic, and potentially harmful. Do you have a link for a how-to?
I just checked the PCV, or what I thought was the PCV, since I don't have a repair manual. All there is, is a hose running from a fitting on the valve cover to another fitting on the intake. Nothing like what I remember checking and cleaning on my old 1977 Corolla. No little ball valve.
I just Googled throttle plate wear. That sounds interesting, although I couldn't find any relevant info that was helpful.
I'm probably knowledgable enough to be dangerous. I can do basic fixes, but don't have a lot of tools other than a socket set and some sundries. As far as digging too far on my own, I'd be concerned that I don't know what I don't know, and screw something up worse!
I appreciate your help! I suppose, if anything, this is telling me I've got to order a manual...
Cleaning the EGR ports/valve is a good idea regardless with the mileage you have. A bit of labor involved, a few gaskets. It requires drilling out the cleanout plugs and tapping them/threading in plugs.
Put the factory plugs in if you can. They are important to the function of the VX's Lean burn. They are NGK brand. It says the model under the hood, but I can't recall it exactly at the moment. I know it's zrf4 something.
I hear you on the high idle helping drivablity. These vehicles are hard to get off the line especially on a hill with the tall gearing. Forget clutching to prevent roll back. However, spec is less than 650 rpm.
Your map numbers may be off from the previous mechanic's "fix." Idle is adjusted via the brass flat bladed screw head on the face of the throttle body (facing the battery). I guarantee yours is seized, as they all are at this vintage. You can get them out with some patience and pb blaster. Clean and re-adjust.
However, your mechanic may have adjusted the wrong place for idle. There should be yellow paint across the threads and nut of the throttle plate spring pivot shaft. This is the point where the throttle cable attaches. Their is a threaded stud and nut with this yellow paint that acts as the stop for the throttle plate. It prevents the throttle plate from ever touching the aluminum throttle body but keeps it closed entirely. It's set from the factory with high precision. If this has been adjusted to increase idle, it will throw the MAP readings off because the throttle plate is open slightly, bypassing the IACV alltogether.
It's really not possible to get this screw back in exactly the right position if it has been changed. If the yellow paint has been disturbed, it has been changed. The problem is, if the throttle plate touches the throttle AT ALL it becomes "sticky" and makes the pedal hard to push initially. Mine was changed by some mechanic at some point, and, after fighting with it for a few days, I bough a new used throttle body from the scrapyard.
Cleaning the entire IM including throttle body, IACV (they can be cleaned, most mechanics will just replace it), egr system, will help for sure.
Thanks, benfrogg. I was looking at a how-to for the EGR at some point, with photos, but I'll be darned if I can find it again. What struck me is the need to re-tap those plugs, which indicates that it's well outside of what I can do, both because I don't have the expertise, or tools. I can suggest it to the shop where I take the car, but it sounds like there's a lot of labor involved.
I'm really discouraged to read about what might have happened to my throttle body, although I've never noticed that the accelerator is difficult to push. I just went outside with a flashlight and checked, and it appears to me that the yellow paint is undisturbed.
I just checked around a bit online, and couldn't find a VX throttle body.
So, it seems the consensus is that a cleaning will fix my ills? This contradicts a bit what my senses tell me is wrong. The strong, cold operation stumbles feel like an electrical/sensor issue, and not restricted airflow. I realize that the IAC and EGR, and perhaps even the PCV may need cleaning for optimum operation, but could they be behind what I've described?
I also just Googled looking for pdf manuals to download. The only links I could find were from questionable sites, and my antivirus and/or Internet Explorer/Win7 prevent me from doing so...if I was careless enough to try.
I can see I'm quickly getting into areas of understanding that are beyond me. What I think I need to do is find a good mechanic who knows what you all do. I realize this is a shot in the dark, but do any of you know of a good shop in the Florida Panhandle or lower Alabama?
I really appreciate the time everyone has taken to offer all the great suggestions! Thank you so much! This is such a sweet car...the shop owner said if I was interested in selling it, it could probably bring ~$4,500 or so. He offered $3,500 cash! No deal!
There are two threads on the throttle body that will have yellow paint on them. One is located on the center of the attachment point of the throttle cable. The other (the one we are interested in) is located to the right of that, where the throttle actually is stopped in the resting position. Does that one still have it's yellow paint undisturbed on it?
Cleaning the EGR ports/valve might be out of your reach. It is a complicated job that to be done right requires pulling the entire intake manifold. It CAN be done on the car, it's just nerve racking that you might lose just one aluminum metal shard from drilling/tapping into the intake manifold.
Will it fix your ills? I'd say 50/50. It's cheaper than throwing parts at it. It's more effective in the long term for eliminating possible problems. Strong cold operation could be indicative of a number of things. During warm up, the ECU is giving more fuel (richer mixture air/fuel) and is running in open loop. That is to say, the 02 sensor is not giving real time data to the computer until it heats up to something like 300 or more degrees (not sure on the actual temp). During that time, the ECU uses preset tables for air/fuel adjustment. That's true both at idle and while accelerating. It is possible, therefore, that cold performance could be better since the engine would be running generally richer and using it's internal tables instead of real time data.
So if that is the case, many things could be to blame. It still could be a sensor issue. The throttle position sensor would certainly be worth testing, as mrmad said. Not to mention the coolant sensor, etc. The reason I'm suggesting EGR's and IACV's is that they are known problems on these cars and yours has enough miles accumulated (and you know it's never been done). Either way, think of having that work done as preventative maintenance akin to changing your oil or spark plugs.
Okay, so back to how the mechanic changed your idle. If the screw has not been disturbed, he did it with the proper method, the idle screw. If that's the case, getting the idle down to spec will be pretty easy. If you want it down there, that is. It'll burn less gas that way for sure. It will also tell you how smooth the idle really is. If you idle it down to spec and it runs rough as can be, you'll have some more clues as to what is ailing the car generally. If it can idle at 650 or less rpm relatively smoothly, the intake, egr, and throttle body are very likely clean.
The mechanic's files over at cartalk.com are pretty good I hear for locating local mechanics with good reviews. I'd suggest someplace that specializes in hondas if possible.
I have a copy of the service manual, it's huge so it's in 6 e-mails. PM me your e-mail and I'll send it away. Be forewarned, it's detailed and has terms/procedures in it that are above my level of skill. It's very helpful, though.