Hesitation while driving/acceleration

Hi, my name is Jonathan, I have a 2001 Ford Focus ZX3 with 87,800 miles on it. Problem: My car hesitates and has trouble switching into higher gears whenever I turn on my A/C. A couple of months ago, it had the same problem, but worse, it actually turned off on me - I put in Mobil 1 10W-30 High Mileage Fully Synthetic oil, and reset the car's electronics by taking the battery out for 2hrs, which made the problem disappear. But now it is back again, but it is not as bad and has not shut down on me yet. It is an automatic transmission type.

Thank you for your speedy answer, it has a lot of info for me to work with. The Engine light is on, and sometimes it blinks and when it does blink it always goes back to solid after a minute of blinking (this is during my driving).

I don't know what a tuneup is, but I change my own oil, oil filter, and air filter. I bought my car used at around 35,000 miles, and since then I've only had the regular "tune-ups" like brake-pad change, wheel rotation, and oil change.

Also, my fuel cap light is always on. But I think that may be a small minor thing, I might have to buy a new cap is all. But besides that, no other lights are on, and the A/C works great even though the car seems to hesitate.

It's been a month since I last updated this question: The CRUISE CONTROL is no longer working, and I now notice that my car engine hesitates when it rains or when I have the A/C on. If I drive it too hard while under these conditions, the car turns off. Can anyone narrow rasmataz's diagnosis? Or offer the correct diagnosis? Please read all my posts (2) so that you are fully informed, I have donated money!

Car stumbles and won't go when under heavy acceleration. When starting from a stop car stumbles but once the RPMs climb above about 2200 it gets better but still persists. Car has no problem at highway speeds until you mash the pedal to pass then it bogs down. I pulled the catalytic converter to make sure it wasn't plugged and problem continued. The hose from the PCV valve to the intake manifold sucks itself closed. I've replaced the PCV valve and the hose with a thicker hose but still sucks closed. My repair manual talks of a secondary inlet that opens under heavy acceleration to allow more air to the engine but I didn't find anything of the sort when I pulled the intake manifold. Any help would be appreciated.

My car is now at 105,738 miles and its giving me a hard time. I am going to be extremely descriptive in hope for a narrow diagnosis and remedy.

1) The car hesitates when I accelerate fast, but it does not hesitate when I accelerate really slow.
2) The car hesitates more often when I drive it in the rain.
3) If the car begins to hesitate, I can press the "Overdrive" button (which prevents the car from going into Overdrive) and the hesitation is reduced immensely, sometimes it goes away completely.
4) If I start the car in 1st gear, then manually move it to 2nd, and then manually move it to "D" drive, then manually turn on the "Overdrive" feature after 45mph to get it to higher gears, then I can reduce the hesitation because I am manually shifting the gears instead of leaving it to the car.
5) I bought brand new top of the line electric spark plugs which reduced the hesitation for a while, but now it is back.
6) I also bought brand new electric spark plug wires at that same time.
7) Driving my car in the rain with the A/C will make the hesitation so bad that it turns my car off.

SO, the fact that the car hesitates more often in the rain makes me feel like it may be that a sensor may be messed up that regulates gas/air ratio. The fact that manually switching my car makes it easier to drive, and the fact that the A/C turns off my car tells me that I also have a power problem, but I don't know where it is coming from.

It's not a dirty fuel injector, its not bad spark plugs or wires, and its not bad oil, oil filter, or air filter.

I don't know, you guys are the pros, help me out! I am giving $5 now to see if this is legit, but if anyone helps me out I will gladly give $50-100 if it is a precise and true explanation of what is going on. If even after this explanation you still don't have enough info, just let me know and I'll try my best to give more.

Thanks for the quick response. I should have included more info. Both 02 sensors have been replaced. Fuel injectors are clean and look good. MAF has been replaced. Vacuum leaks are not an issue all hoses are new and many clamps added.
Ignition wires, plugs, coil have been replaced.
I will run a chemical that will get the possible water and alcohol.
The part the intrigues me is the TPS which hasn't been replaced but more so the MAP sensor. What exactly does it do and would it being defective cause the hose from the PCV valve to the manifold to suck itself closed? Both those parts are new so I now it isn't a stuck PCV valve and when it is disconnected smelly air does come out of it. Almost as if the manifold is sucking too hard on it. Any thoughts on this secondary inlet that opens that can accessed during heavy accelaration. Any help is great.

On a cold start the engine spikes a high rpm like it normally does and then comes back down and everything seems fine. Once the engine warms up, the problems start!

On a warm engine, the car idles really rough. Almost feels like it wants to stall. If you give it a little gas (while braking) then it overcompensates and the idle hesitation goes away.

During acceleration there is a very subtle 'grab' when running in the lower gears. It's not very noticeable but it 'grabs' or 'hesitates' slightly during acceleration. Maintaining speed it seems fine and I don't notice any fluctuation. Running in the high gear/rpm (55-65mph) I don't notice it.

About a day later the CEL threw p0171 (system too lean bank 1). The very first thing I did was replace the upstream/pre-cat O2 sensor and then cleared the code. The CEL didn't come back but the original problem didn't improve.

I took the Idle Air Control off the throttle body and cleaned it with carb cleaner. I dried it and put it back on. I also cleaned the choke on the throttle body. That didn't seem to help, plus running the engine with the IAC unplug made it worse so I figure my IAC is good.

Next, I thought it might be a misfire so I replaced all four plugs and wires. That didn't fix it so the next thing I replaced was the ignition coil because the primary coil tested on the high side of the ohm tolerance (.9 sometimes 1) without a load. That didn't fix it either but did seem to improve the overall hesitation for about a day or so (about 50 miles worth). I thought I might have fixed the issue until it returned a day or two later.

So then I decided to replace the fuel filter. Didn't improve anything (still no CEL the whole time). Next thing I did was change the oil and oil filter. No dice.

So then I started thinking vacuum leak. I walked all through the intake process and I found a dislodged pcv tube (dislodged where it connects to the air filter) and an EGR tube seared at the manifold.

I reconnected the pcv tube and used epoxy to secure it to the air filter box (because the plastic OEM grommet was broke). I ordered a new EGR tube and replaced it (yes, I reconnected the crank case breather tube). After all that, it didn't improve the original problem but the engine noise, smell and gas mileage was much better because of the new EGR tube!

So at this time I can only think of two other things that could be the issue. Injectors or MAF sensor.

Figured I would go after the injectors first. I chose the easy route. I treated with a bottle of Lucas injector cleaner. Believe it or not, for the first 30 miles or so after the treatment. The original problem was almost gone. Just a very subtle hesitation at idle. But only if it idled for a while, not right away like before. I thought that was it. Some dirty injectors that were now getting cleaned up!

About a day later. The 'hesitation at idle/grabby during acceleration' was back and just as bad as ever and the CEL lit back up with p0171 (system too lean bank 1).

The only thing I can think of at this point is the MAFS. So I grabbed a Security Torx and took it off and disconnected the harness. I hosed it with CRC MAF cleaner, left it dry and reconnected/installed it. That didn't fix anything.

Just a little bit ago I was doing some more testing with the MAFS and here is what I found:

The engine seems to idle better/different with the MAFS disconnected, when I reconnect it the problem returns. I know that the engine will run rich without it so I didn't do it for very long, just to test. Without the MAFS connected it still idles rough. But not near to the point that it does with the MAFS connected.

The other discovery I made was that if I remove the MAFS from the intake hose (and set it on top of the hose) but still leave the wiring harness connected the engine seems to idle much better and I don't notice any issues. Moving the MAF too much while outside the intake hose seems to causes unexpected air flow and kills the engine.

I'm at my wits end. The MAFS is like $137.00 for my engine so I don't want to replace it unless I need to but I'll happily do it if that will fix this issue. What do you guys think?

Wow you did a lot of work! I'm no mechanic but I read your post because I had a similar problem, but mine was fixed with a new ignition coil. But as it is, your problem isn't with the Ignition Coil. Well, I replied to your post to hopefully bump it up on the thread so a mechanic will take a look at it, I hope you get it fixed soon! (If you donate like $5 you will get an answer within 3 days, just so you know)

Got a 2000 Focus, 2.0 zetec engine stumbles/hesitates under acceleration/load. Idles ok and I can rev up the motor just fine when not in gear. Replaced the dpfe sensor, spark plugs & plug wires. No improvement. What is the culprit? I have read a lot of forums where people had the same symptoms as mine and it was the dpfe sensor for the EGR. I have also checked for vacuum leaks using propane gas around the intake and vacuum hoses with no change in the idle. Please help!

Thanks for the suggestion on the coil pack. I did replace it a few days after my original post. I took off the coil pack and had it tested at Autozone with a multimeter and they said there was nothing wrong with it, but after thinking about it, all they can test for is if you have continuity in the coil. They can't test for performance under load. So I replaced it despite their "professional" advice to look elsewhere. Guess what Autozone, the coil pack was bad.
Car runs like a top now.