1999 accord severe hesitation/stumbling when hot
 

Hello all I'm new here. I've been doing my own mechanic work for years now and have a decent understanding on engine repair. My girlfriend has a 1999 honda accord 2.3L 4cyl automatic. It runs great and has been a decent car until last week. When the car has been running for a while ( 20 or 30 minutes) it starts bogging down and stumbles during load/acceleration. When you first start the the car, it runs great. No sigh whatsoever that something is wrong. If you lightly press the throttle down, it accelerates fine, but while climbing a hill or pulling into traffic, it acts like it's flooded or something. Here is what has been done to the car: new distributor, cap, rotor, wires, plugs, pcv valve, air filter, egr port and upper intake manifold cleaned, throttle body cleaned, new power steering pump, new valve cover gasket, ignition switch.... all in the past 10,000 miles. I guess the fuel filter is attached to the pump so I haven't changed/cleaned that. I just need a little help figuring out what could be the problem. I've tried unplugging the front O2 sensor to see if there was any change but all it did was throw a CEL. Most if the time the CEL is off but when it starts running really rough, it comes on and starts flashing. I had the codes ran and it was just a bunch of misfire codes for all the cylinders. One thing I did notice is the temperature gauge stays stuck just under the normal operating temperature. I don't think it ever moves. The radiator fans come on so I'm assuming it is either a bad ECT sensor or gauge. Someone please help push me to the right direction. I have checked for vacuum leaks and haven't found any .... how do I test some of the other sensors? Thank you sooooo much
2 things I forgot to add... this hesitation /stumbling goes away above 2000 rpms and she did run the engine down a little on oil one day( maybe a quart or two) I read about this affecting the vtec and acting like a fuel cut. Please help. Any help would be much appreciated.

You did a lot of work to this car. Did the current problem start before or after any of these repairs?

Do you have a scan tool that can read live data?

About 6 months ago she had the distributor/wires/plugs/cap/rotor changed because the shop that she took the car to " found them to be defective". The valve cover gasket because it was leaking. In the end all that was wrong with it was the ignition switch. Pretty much everything that has been done to this car was done like 6 months ago. Yesterday i did the pcv valve, and pulled the upper intake and scrubbed every inch of the inside of it. (Might as well since I had it off to clean the egr port) Just today I've pulled the fuel pump and checked the filter/screen and it's nice and clean. I also disconnected the catalytic converter to make sure it wasn't clogged. I recorded a small video of the car acting up today if it helps. I don't have a scan tool that reads live data and I disconnected the battery so when I had the codes ran today, there were none stored. I'm thinking that it may be one of the sensors since it only does it when it's been driving for like 20 minutes. Maybe intake temp sensor, coolant temp sensor or map sensor? How about the ignitor or coil? Are there ways to test these with a multimeter? I guess it's possible that the distributor they installed is now defective.

Until you get some codes, don't replace any more parts. Once the codes return, post the actual code on here.

Sounds like me: Got a problem? Throw parts at it. Try the upstream O2 sensor next. No guarantees, but my 95 Accord had similar issues last year. Replaced the sensor and it ran like a champ.

Funny...we have the same Honda, but I had a similar issue with a different vehicle.

I don't know much about the part itself but I had a similar problem on my Chrysler in September where the EGR valve went bad, and would roughly idle, kick and kill the engine when idling or at low RPM, especially when first starting up. I would have to get it started (which it wouldn't even want to), then immediately rev the engine above 2000 RPMS to keep it alive, quickly throw it in drive and take off, or else it'd die. Replacing the EGR valve fixed the problem completely.

Before that however, the valve cover gaskets had been leaking, but after a while both the head gaskets blew. Not only that, but a wire running from the thermostat to the gauge had been worn away (if I remember correctly) and wasn't giving me the correct temperature on the gauge (maybe this is a problem you're having too?). It was reading as normal...then one day the thermostat shot up past the red tick mark and I started smelling burning oil, then saw smoke. That whole time, no lights came on (check engine etc), fans were running fine, etc.

To me it sounds a lot like the EGR valve. Hope my response helps.

PAHonda: There has never been any codes when doing the jumper and continues to stay that way... otherwise it would be easy!

VinnyBuffone: I had a guy who does smog in california looked at it. He suggested map sensor or clogged intake housing where the vacuum tube from map goes in is clogged. I'll let you know what happens when I try all that.

The problem started before any repairs, and still so far no change yet... getting ready to replace the tps and maybe the map sensor if its vacuum hole isn't clogged.

its really easy to start replacing parts and hope that you get lucky, in my humble opinion that's a possible waste of money,,
you need to diagnose what is at fault exactly before you start replacing parts and hope for the best ,,, well ,,,,unless you got a lot of money
Everybody wants to BAM BAM fix car issues ASAP but sometimes it takes time and proper diagnose,,, i realize that it is a pain, been there done that
chk for possible causes and start the eliminating process ,,