Help! I have a 1990 Accord LX, 2.2, 5speed, 236,000 miles. It has developed a miss on acceleration between approximately 1500 & 2200 RPM, only when warmed up. Above 2200 RPM it runs fine, cold or warm. This began after I blew a heater hose and didn't notice until the temp gauge was at the hot mark. I coasted the rest of the way home (1 block) and the next morning replaced the hose and refilled with coolant & distilled water. Only took about 3 quarts and started right up and seemed to run fine. The next morning driving to work, it ran perfect until operating temp, then I felt a slight miss when I tried to accelerate. This problem got progressively worse. I pulled the plugs and cleaned them, and change the cap and rotor. After that it wouldn't start at all! I had no spark to any of the plugs. I checked the resistance of the coil and it was fine. I got my Haynes manual and was following their procedure to check the igniter with my multimeter and I notice one of the wires that connected to the igniter had broken insulation and green corrosion in the wire. I replaced the entire distributor with a brand new (not rebuilt) unit, and the car started right up! Upon test driving however, I was back to the original problem - - misfire under 2200 RPM when accelerating (the engine was already warm). The following morning I installed new plugs and again it ran perfectly - - for a couple miles until the temp gauge got about 1/3 the way up, and it started doing the same thing. I saw a TSB about clogged EGR ports possibly being the cause, which said to pull 10" vacuum on the EGR valve-- if the car stalls this isn't the problem. Well it stalled. Even so I went to step 2 and plugged the EGR vacuum line and test drove. Problem still there. Any know where to look next? I'm thinking possible Coolant Temp Sensor or Oxygen sensor but when I unplug either one nothing changes. A buddy suggested a dirty Idle Air Control valve? That doesn't sound like it would be temperature dependent to me but I'm going to try cleaning it anyway. Suggestions?

 

Clean the EGR ports. The rpm range of the misfire & it happens when the car gets to operating temperature and switches to closed loop is pointing to the EGR ports.

I did the vacuum test on the EGR valve and stalled out my 95 engine. Only one port was slightly open (95% plugged) while the others were completely plugged.

 

Thanks for the info. I should clarify however, even though the vacuum test said the EGR ports weren't the problem, I plugged the EGR vacuum line and test drove the car. I did get a CEL (expected) but the problem remained even with EGR disabled. Do you think it could still be clogged EGR ports? And why would this problem occur suddenly (instead of gradually over time)? Please understand I'm not trying to discredit your input, just trying to learn how these beasts work! :-)

 

EGR essentially takes exhaust gas and puts it into each cylinder to improve combustion (better fuel mileage and power). The 90 accord doesn't have a knock sensor and the computer may not set a misfire code due to loss of exhaust gases.

My guess is that 1 cylinder is getting some exhaust gas and others are not making the stumble much more noticeable.

Cleaning the EGR ports is not too difficult and essentially free to do. Once you get the ports and the chamber clean, then you can rule out EGR if you still have an issue. It is certainly possible you have multiple issues. Need to rule out EGR first.

Here is a good video on how to remove the egr plugs and describes the system.

 

Another video on a 94-97 accord that is similar.

 

Thanks for all your help. I guess I'll clean the EGR ports because nothing else I've tried has worked and the symptoms are exactly what I'm experiencing. I understand why the test may show a false result, as you mention they all may not be plugged. But wouldn't the problem go away when I unplug the EGR valve and plug off the vacuum line? (in fact this video even mentioned that their problem went away when they did this). I'm really starting to dislike this car!

 

Thought I'd update for anyone with a similar problem. My issue turned out to be spark plug wires. When this problem first started, I thought maybe the spark plug tube seals were leaking and causing a misfire. I had a small amount of oil in there but it hadn't gotten past the threads, but 3 of the 4 rubber seals on the bottom of the spark plug boots were destroyed and I had to pull them out with needle nose pliers. I had cleaned the boots and installed new plugs, but left those seals off. I thought that may cause a misfire, but the car ran beautifully until it warmed up so I checked the plug wires off my list of possibilities. They were NGK wires with only about 20k miles on them. Yesterday after checking (again) for any loose connections or vacuum leaks etc., I started the car and started driving around the neighborhood. Made it almost 10 minutes but sure enough as the temp gauge approached the 1/2 mark, the misfire appeared, and as usual seemed to get worse the more I drove, especially with the A/C on. I had previously picked up another set of wires that I was planning to return, but out of frustration and being out of ideas I went back home and installed the new wires, with a little dab of dielectric grease in the spark plug boots and distributor terminals. Misfire is completely gone! I've driven 25-30 miles now with the engine fully warmed up and with the A/C on, and the issue hasn't come back. I understand how those seals being missing could have been the culprit, but what I don't understand (and what threw me off track) is why did it only misfire when warm? I would have thought it would have done it when cold as well. I can't explain that part but I'm glad my problem is solved.

 

I've had the opposite experience where it gets better when warmed up. I guess this shows you shouldn't ever rule out something because "they don't usually fail that way".

Maybe you could've seen visible arcing from the wires, with the car running in complete darkness.

 

Didn't seem to misfire at idle, just between 1500 - 2200 RPM. And you can't really see down in the spark plug holes due to the seal at the top of the spark plug boot. I'm just glad it's running right even if I can't explain it :-)