project5k

The back-story:
97 civic ex, D16Y8, OBD1, 5spdman. AEM cold air intake, Headman 4-2-1 header, otherwise bone stock under the hood.
260,000 + miles
NO CODES, NO CHECK ENGINE LIGHT(key on test proves it works)

A couple months ago i was driving along on the highway, and started having a problem with the throttle. After playing with it for a few miles, i found that the problem was a "DEAD SPOT" in the TPS. Right at 3kRPM more or less gas and the car was fine, but in this spot it was just like i had totally removed my foot from the gas pedal. Ok, this is easy, did the research, dremeled the "rivet screws" and replaced the TPS.

Life is good. Problem is gone.

Yesterday I'm on the way to a new job and the car hesitates again..(2 miles from the house, so I'd say car was probably up to temp) just like it did before, only this time i cant detect a for sure dead spot like before. its not a spot, but a range. again i was about 2500rpm... I cant say for sure if i moved the gas pedal that caused it to start hesitating or not this time, but if i did pumping the gas pedal only resulted in feeling the engine go from an obvious coast to a full throttle load condition. small movements didn't do anything, so i moved the pedal more and more till i was going about idle to FT... then after a second of this mess, the car seems to drive fine. Its almost like there's some piece of trash floating around inside the tps.

Then, again, on the way home from the job, about a 1/4 mile into my trip,(car prolly wasnt fully warmed up) i have the hesitation again... pumping the gas pedal didnt seem to really do me any good(i know pumping does nothing on fuel injected cars, i'm doing it to try and clean/clear the tps) then no more of this problem anywhere in my 70+ miles home I couldn't CAUSE it to happen by moving the pedal like i did before i replaced the tps...

The other thing that happened yeserday that was a new one, just shortly after having this throttle position/hesitation event, i ended up stopped at a light, and the idle was dead on at 2k. Tapped the throttle up to 3500 and idle fell back to the 750-800 range. never did it again. definately not a sticky throttle cable.

Car starts and idles perfectly, restarts and idles warm just fine... when its working, its working, but this hesitation and unpredictability stuff is a safety issue...

Don't think its fuel delivery, long hard high rpm runs didn't result in hesitation,

Maybe ignition? but again, if a sparkplug or wire were getting weak, i'd expect problems under higher load conditions... Both times i had the hesitation yesterday was early in the drive, and was in a neighborhood kinda area, so 35-50 mph, just normal driving...accelerating in 3rd kinda stuff... once i'm in 5th, stretched out on the highway doing 75-80, turning over 3kRPM she runs like a dream...

The only other thing that i can think of that would play like this might be O2 sensor. As the car goes from open loop(cold computer map) to closed (actively reading the O2 to control fuel delivery) if as the car is warming up, and the O2 is weak, and not up to temp, it may be sending momentary bad data to the computer till it warms up... but I'd think I'd get a CEL or a code from this... I remember a few years ago i had a code and CEL and replaced the O2 sensor myself and all has been great since, so at least i know the O2 isnt forever old(i remember having to extend the wires cause of the header)

need my daily driver to go to work...
really appreciate it

project5k

wow, 140 views and not a single reply.

Drove the car again yesterday afternoon to test it, went around the block here in the neighborhood, no problems, car was up to temp, so i took it out on the big roads, all was good, tried long slow accels from 25 up to 60, tried high rpm rapid accelerations, tried everything i could think of to get it to fail, and nothing... not a burp.

Now i'm more worried than i was before. Intermittent problems are the hardest to chase down.

I'm afraid to let my wife drive the car for fear it may cut out on her in a passing situation or something.

anybody got anything i can check? I'm good with tools, Voltmeters and such, i've got a haynes manual, I've just run outa things to try...

Mtzking

Hey I had the same problem with my 98 civic coupe, I had this problem for quite a while. What I did was advance the timing just a couple of degrees and since I had just replaced the idle control valve less than a year ago I removed the intake and sprayed some brake cleaner inside the hole before the butterfly valve in the throttle body that leads to the idle control valve and let it sit for a while. Since the car as hot the brake cleaner bubbled in there for about 30 seconds. Five minutes later I turned the car on and drove it a while until it got to operating temperature and it hasn't done it since. Hope this helps