Hard start and rought idle/power loss

[Morgenster]

Maybe for a day I think.
Coughing is also strange. Sometimes there is no coughing, sometimes it starts coughing badly (but again only when I am braking with engine).

Are things getting worse?
Engine braking should cut off fuel and spark so the engine shouldn't cough when you do that!

[shrike071]

It could also be the DME itself going out. Electronics do all sorts of odd things when they begin to fail...

[t_marat]

how strange it is, but it coughs only while braking with engine. meaning releasing the gas pedal while in motion in say 3rd gear. by coughing I mean the puffing sound that comes out of exhaust (?).

[t_marat]

it is becoming worse. Mostly starting the engine takes 3-4 attempts; it just won't fire up; or starts up, but rpm is close to 0, pressing the gas doesn't make any difference. and more strange is that sometimes it starts right at the first try.. Also engine pings a lot more than it used to. But it could be related to temperature, it is really hot (around 100F, 35-38C)
I am inclined to change the crankshaft sensor. could it be the culprit? does it do things like this?

[Morgenster]

Wouldn't hurt changing it. Did you try a second reset?

[t_marat]

I used an injector cleaner called Gunk Carbuerator and Injector Cleaner. It definitely made a difference. For the past 5 days I didn't have trouble starting the engine, it would start immediately. Though, I can't say it is gone totally, yesterday I had to do a second try as it wouldn't start on first attempt. But that was the only hard start in the past five days.
However, problem with stumbles on acceleration is still there. Today tried resetting the ECU. Till afternoon it was fine, but then it stumbled again. And I don't really think resets have any effect, because problem seems to appear randomly. For example on the evening car drove without problem, even though during afternoon it had problems.
One thing, when engine starts stumbling, flooring the pedal helps. It starts accelerating normally. And as I wrote before during hiccups like that engine idles rough, and exhaust turns into black (not very black). Problem seems to appear mostly when engine hasn't fully warmed up. Mostly, not always.
How can I disconnect the oxygen sensor? Bentley says the socket is on the left side of the engine, under the starter. Looked into that area but there are some many things in there, couldn't find the connector.

[Morgenster]

I used an injector cleaner called Gunk Carbuerator and Injector Cleaner. It definitely made a difference. For the past 5 days I didn't have trouble starting the engine, it would start immediately. Though, I can't say it is gone totally, yesterday I had to do a second try as it wouldn't start on first attempt. But that was the only hard start in the past five days.
However, problem with stumbles on acceleration is still there. Today tried resetting the ECU. Till afternoon it was fine, but then it stumbled again. And I don't really think resets have any effect, because problem seems to appear randomly. For example on the evening car drove without problem, even though during afternoon it had problems.
One thing, when engine starts stumbling, flooring the pedal helps. It starts accelerating normally. And as I wrote before during hiccups like that engine idles rough, and exhaust turns into black (not very black). Problem seems to appear mostly when engine hasn't fully warmed up. Mostly, not always.
How can I disconnect the oxygen sensor? Bentley says the socket is on the left side of the engine, under the starter. Looked into that area but there are some many things in there, couldn't find the connector.

O2 Very hard to get to unless you're especially limber. Black exhaust pretty much tells you your car is literally choking. So that means either intermittently missing spark or FUBARed air/fuel ratio. Not a mechanical problem IMHO. Intermittent (both cold and warm) points to electrical problems. I still think O2 sensor or just maybe intermittently failing MAF or TPS. A diagnostic trick in case you don't have good known replacement parts and you think failure is intermittent: hook up a multimeter to the wiring on these sensors and check what happens on the multimeter with the engine running until it happens. If you're really handy you can hook it up so you can keep it in the car and drive.

EDIT: almost forgot: when you tested the TPS, did you test resistance range in motion from fully closed to open and back? Also, testing the sensors might not be enough, you might have to test there respective connectors at DME level to check for intermittent circuit breaks.

[t_marat]

O2 Very hard to get to unless you're especially limber. Black exhaust pretty much tells you your car is literally choking. So that means either intermittently missing spark or FUBARed air/fuel ratio. Not a mechanical problem IMHO. Intermittent (both cold and warm) points to electrical problems. I still think O2 sensor or just maybe intermittently failing MAF or TPS. A diagnostic trick in case you don't have good known replacement parts and you think failure is intermittent: hook up a multimeter to the wiring on these sensors and check what happens on the multimeter with the engine running until it happens. If you're really handy you can hook it up so you can keep it in the car and drive.

EDIT: almost forgot: when you tested the TPS, did you test resistance range in motion from fully closed to open and back? Also, testing the sensors might not be enough, you might have to test there respective connectors at DME level to check for intermittent circuit breaks.

Why didn't I just disconnect the MAF when the engine was running rough, should have checked that long ago.
I did test the TPS in motion with digital multimeter. Seems to be normal, linear.
I don't think its circuit breaks. If that would be the case, flooring the pedal should be of no use, correct? or not?
tomorrow going to have the intake manifold taken out and look for vacum leaks. along the way will try running without o2 sensor.

[t_marat]

Had the intake manifold removed and inspected for vacum leaks, none to speak of. intake gaskets had been replaced, hoses also inspected, and it turns out I have no air leaks. a really comforting thing.
tried disconnecting the MAF, but engine keeps stalling.
After that disconnected the O2 sensor. Got disappointed as engine was idling a little rough. Went for a drive, first thing I noticed there was no pinging. Lately engine had been pinging a lot. Drove around for about an hour, had no problems! interesting is that pinging dissapeared as soon as the O2 sensor was disconnected. Could the pinging be also because of the O2 sensor?
Should have checked the O2 sooner, especially it was advised as one of the possible reasons.
Thanks everybody for help.

[Morgenster]

Well I guess it could: fake signals from o2 could maybe have the DME make the mixture leaner and heating he cilinders somewhat more than average. Let's hope the o2 fixes the problem.