Hard start and rought idle/power loss

[t_marat]

Since last November I started having problem with starting the engine in the mornings, especially when it was cold. It would take a lot more cranking (3-5secs) and run rough and stall. What I did was to press the gas and hold at about 1000-1200rpm for about 40-60seconds, then it would idle normally, without roughness. Back then I changed the spark plugs, they were oily. Changed the valvecover gasket. But still had this problem.
Now the weather isn't cold. In the mornings sometimes it starts right up, about 2 secs of cranking. Sometimes I crank for 3-5 seconds, it won't start and I let go. Interesting is that right after that it starts immediately, have to crank for maybe 1.5seconds. This wasn't causing me much problems and I just ignored it. But today engine briefly ran rough and lost power while fully warmed up. This lasted for something like 1-2 minutes, then back again normal. My brother took the car after that and says that car actually stalled when he switched to neutral.

What could this be? During winter holding the rev at 1200rpm for a brief period made the engine ran normally. Because of that I tend to think it is something close to the combustion chamber, as in 1 minute area near it gets warmed up. I already changed spark plugs (Denso, by catalogue), so could this be injectors or ignition coils?

I read postings about fuel pumps. Could this be a fuel pump?

[mamilapon]

Pull the valve out and give it a good clean with carby cleaner.Also use a digital meter to check if youre getting 12v.

[Morgenster]

When you started in cold mornings and managed to without applying throttle, did the idle jump to 1600 and then drop to 1000?
If it just dropped lower than that there's a sensor out of whack. Could be anything from TPS to MAF, etc. I'd suggest checking for vacuum leaks or sensors out of tolerance.

[t_marat]

Mamilapon
By valve you mean ICV? Where from to measure the voltage, at the battery? The battery is OK.

Morgenster,
In winter engine would never start and idle by itself, I always had to keep the gas pedal pressed a little. Otherwise it would ran really rough and stall.
If it was TPS, then I shouldn't have rough running and power loss when the car in gear and going forward? As far as I know TPS is there to tell the ECU to engage the ICV, and has no effect when I am pressing the gas.
Doubt its a MAP, but could be. My previous was dead, changed a more than a year ago.

I tried spraying around carb cleaner. Couldn't see any difference in rpm.

[Morgenster]

What happens after a full DME reset (battery disconnect for 30 min)? Does the idle bounce or move at all when running warm? I'd still try multimeter tests on those sensors including temp sensors on the engine. If those all check out I'd work my way to more mechanical issues like the icv, fuel pump, FPR or filter. BTW: were the plugs oily on the firing side or on top? If they're oily on the firing side things are looking slightly worse.

[t_marat]

The plugs were fully covered in oil. I think it wasn't the firing side, its just the oil accumulated in the spark plug socket, while removing the plug it just covered it all. Today I checked the spark plug sockets, and they are pretty clean (changed valvecover gaskets couple of months ago).
Checked TPS resistance values. They were 1.3kohms to about 4kohms. Bentley says it should be in 1-4 kohms range. So I disconnected TPS sensor and drove like that around for about 30 mins (its 90F/32C in here ) Engine did not stall. But if you are say in 3rd gear, release the gas pedal and press it again, then there is some wobbliness in acceleration for a short while.
Went to a local shop to buy a new one and was quoted 150$ for a new one. Very expensive for a simple variable resistor. Anyway of cleaning it?

edit: can a TPS be blamed for rough running (not just idling) and loss of power?

[Morgenster]

Mine has a range of 1,8k to 5k and it works so I wouldn't change it just yet. And you can get them less than half that price anywhere else. It could still be bad and cause rough running if the voltage differential isn't continuous from idle to WOT. Changing engine temperatures can maybe obscure faults with electricals because they do not necessarily show up when cold (or the other way around). Did the reset change anything? Because when I did it some two or three times after changing the valve cover gasket and plugs it ran great all the time.

[t_marat]

I did the reset yesterday, left the battery disconnected for the night. Cleaned the crankcase ventilation connector with a carb cleaner, as it was very dusty (leaking slightly).
So far I did not have any problems, car did not stall and no rough running/power loss. But I guess its too early to say for sure problems are gone.

[Morgenster]

You might get lucky or not. But if the problem gradually returns it's most likely a DME sensor out of tolerance. Doing the reset right after plug changes or any engine work can help the engine adjust to different running conditions, so if you didn't do this when you changed the gasket and plugs it could stay good.

[t_marat]

Problem is back, nearly stalled this evening (even though it drove wonderfully during the day). Again the same thing, try starting the engine, spin for about 4 seconds, give up. Right after that it starts immediately.
I don't think engine is stalling due to ICV. Last year I had the same problem with engine stalling, cleaned and changed ICV to no help. Changed MAF and problem was gone.
Last year I also had a fuel pump failure. It might be unrelated but it failed at exactly the same time as engine stalled. I switched to neutral and was taking a left turn.