Hey, guys, I'm new to this forum and have a problem that I'm hoping someone can solve. My car is near mint condition with 143K miles. It runs perfect during warm up but after reaching full temp it stumbles as the accelerator is depressed. Before pressing the accelerator, the engine purrs with perfection. Once the RMP reaches about 1500, the stumble goes away. If I press the pedal aggressively, it's almost undetectable. I am not 100% sure whether this is an electrical or a fuel issue. I wired a timing light to each plug wire and drove the car slowly on my street at night with the light on my windshield (trigger on), and couldn't detect any misfire visually. I did however replace the coil and igniter in the distributor which made no improvement. Initially, I thought this was a faulty FI temp sensor, so I also replaced that and again: no improvement. I've gone through the Haynes manual doing the various FI checks. The throttle body, Idle Air Control (IAC) valve, Fast Idle Thermo Valve all check out fine. My car does not have the Intake Air Bypass (IAB) system. Lastly, I checked the O2 Sensor, and it checks out fine. So, I have done all I know to do and am at a loss. The car is drivable, but this irritating stumble has me stumped. Any ideas?

 

If the stumble happens around 2200 rpm, then I'd clean the EGR ports in the intake manifold. It is a common problem on 90-97 Accords. The hardest part will be removing the caps to expose the ports. A small slide hammer is ideal, but you can use a long screw with a washer and a socket as a DIY slide hammer. Watch some youtube videos on the 90-93 accords to get an idea of what is required.

I'd avoid changing sensors unless you are getting a check engine light and/or the sensor actually tests bad. Too often throwing parts at the car can make matters worse, when cheaper aftermarket parts fail out of the box. Then you have 2 problems to troubleshoot, and folks always assume the new part has to be working properly. If you gamble and put a new part on, keep the old part, as it may be working proprely.

 

The stumble, is below 2200 RPM. It is pretty much gone at around 1500-1700. Like I said, if I stomp on the accelerator pretty hard, the revs climb fast enough that it seems almost normal. It's when I'm pulling away from a stop in a slow, gradual manner. I agree that I shouldn't throw parts at the problem, but I can always change them back out and plan to do so since I removed Honda OEM parts. I forgot to mention that my check engine light is not on. Any other input?

 

The range the EGR port can open is ~1700-2200 rpm, so this could be your problem. Clogged egr ports in the intake is a common issue on 4th and 5th gen accords, so you likely need the service. My 95 accord ports were partially to fully clogged at ~150,000 miles and caused a slight stumble. Clearing them resolved the stumble.

I post warning about changing out parts without diagnosing to help folks save money. Members in the future will see your attempts to fix the issue and may try these as well. I assume members are cheap (like me) or don't have a lot of disposable income to take their car to a shop (like me in the past).

 

I agree that I shouldn't throw parts at a problem and I usually don't. I actually tested the water temp sensor on the stove and it seemed to have a change in ohm reading as the water came up to boiling, that made me think that was the problem. But, I didn't test the replacement sensor (aftermarket), to verify it was working properly. I will try cleaning the EGR valve because it probably needs cleaning anyway, as you suggest. I'll report back in a few days.

 

Cleaning the valve may help, but make sure to get into the intake manifold and get the ports cleaned that are downstream of the valve.

 

I performed the EGR tests as described in the Haynes Manual. The valve held vacuum and when vacuum was applied the engine stalled. I also checked the EGR solenoid which also passed. I did not remove the EGR valve nor did I clean the intake as suggested, because it seems to me that if that were the problem, the engine would always stumble, but it only does so after reaching full temp. It runs perfectly when cold. Am I thinking about this logically, and if so, any ideas what to check next?

 

It is the EGR ports.

EGR isn't activated by the engine computer until the engine warms up to operating temperature. The valve holding vacuum means the diaphragm is not torn and operates. The engine cutting out when opening the EGR valve means not all the ports are not 100% clogged. You will find 1-2 ports completely clogged, while 1-2 are partially. The EGR valve opening sends different amounts of exhaust gas to each cylinder and causes the stumble when you are at operating temperature. I did the same tests as you on my 95 accord that is basically the same engine as yours. Got the same results as you and still had partially/fully clogged EGR ports that solved the same stumble issue.

 

Did you remove the manifold to clean it, or just use a spray?

 

The 90-93 accords are harder to clean out. You don't have to remove the intake manifold. You will need to disconnect the fuel rail and get it out of your way.

There are 6 plugs on top of the manifold that you need a slide hammer to remove. You can use a long machine screw and a socket with a washer to make your own. You will have to drill into the plug and use the slide hammer to remove. You may want to get replacement plugs when you do this job.

A shop vac and a drill bit (by hand) are best to clean out the holes. You can try brake cleaner to get the passages cleaned, but the 90-93 are not simple to access.

Before attempting, watch some youtube videos on how to clean the EGR ports for your car. The 94-97 accords have an access port to make cleaning much easier. Your accords will have the plugs and will require a slide hammer to access.