Rep Power: 0

I don't know exactly where to start so I'm just going to jump in and hope I can explain my issue so it make sense, here's a little history on me and my car. I've been a mechanic for a little over 3 years now and I'm still learning a ton of new things every day so bare with me. ok, so about a year and a half ago I purchased myself a 2001 honda civic EX 1.7L with an AT trans that someone was selling because it had an overheating issue, long story short the head gasket had a small leak at one of the coolant passages allowing combustion gasses to enter into the cooling system and over pressurize it which I was able to fix with a new head gasket.

The car also had connector issues on the CKP causing it to randomly go into limp mode, and has a few other issues that need to be addressed. With all that being said here's the main issue I want to fix and has had me baffled for a while now, the car seems to have slow acceleration at low speeds and when passing, and sometimes odd shift timing, so for example if I'm trying to take off from a dead stop I could put the pedal all the way down and it will slowly climb then randomly kick down and gain up to 5000RPMs, the same issue takes place when trying to pass, say if I'm cruising at 60mph and I want to pass it feels like it barely wants to accelerate but randomly it will kick down.

I can't tell if its the engine or transmission that's the problem, I want to say the trans is slipping/not shifting properly but then again I'd hate it to be something as simple as a sensor on the engine giving the trans false info like WOT. I just want to see what suggestions everyone has before I make a move foward trying to fix my issue, I'm sure the car could use a new TPS and IAC but before I go that route I want to see what everyone has to say. Also, I did replace the throttle body with a junk yard one because I was having bad idle surge, the problem went away for the most part but has slightly come back where the idle jumps when sitting parked.

 
Rep Power: 211

Idle jumping: remove the iacv and clean it and the gasket screen with brake cleaner then reinstall.

Slow acceleration: Sounds like a possible transmission issue. You may want to try a 3x3 ATF drain and fill. Also, you may want to remove and clean (brake cleaner) the transmission shift solenoid(s).

 
Rep Power: 126

Any codes? Can't recall the code off the top of my head but there is a code that is considered the "death code" for these transmissions.

 
Rep Power: 0

I also believe its a transmission problem because I had the same year/make/model Honda at my work yesterday and just to compare apples to apples I test drove it and of course it accelerates as I feel it should and confirms my suspicions that I do in fact have a problem. As for any codes last time I checked it was throwing an O2 code but Its been a while since I checked, but once I do I'll post all codes here, thanks.

 
Rep Power: 367

failing O2 will throw more fuel into the cylinder, so unless it is throwing so much than it floods...

 
Rep Power: 229

If there is a transmission code usually the "D" on the shift assembly flashes.

The o2 could definitely cause your power delivery issues. Lean is mean, rich is slow, it will go rich to protect the internals if it can not read o2 properly, as sdaidoji said.

The power delivery issue could then cause transmission symptoms as the, now lower power band, would affect torque delivery, per rpm range, this torque/rpm curve is mapped to the automatic gearing.

So if the pcm is wanting to see 127hp and 90 torque at 6000rpm, and the transmission selects third gear... and now with the o2 issues causing a refuel, the pcm sees 100hp and 70torque, for the same 6000rpm, it could select different gearing to adjust for the issues.

Make sure to replace it with an OEM sensor or the same part direct from Denso, the generics almost always cause issues.

 
Rep Power: 367

at the least, the 01-02 have the cheaper narrow band sensor