ok, the vacuum hose to the fuel pressure regulator modulates the fuel pressure, so its lower at high vacuum, and higher at low vacuum (aka wide open throttle).

not wanting to read over this 4 page thread again, can you recap the *current* symptoms ?

 

Symptoms:
Starting the car occasionally is hard. Sometimes one crank and it starts up like a brand new car (no kidding). Other times I have to crank it longer to start. It will start every time - 4 to 5 seconds at most to get started. If its one of the longer cranks - it will start up and shudder and then slowly settle into a smooth idle.

In idle - till the gauge reaches about 1/4 on the scale - if I floor it abruptly its fine. past 1/4th and upto 1/2 (operating temp) if I gently press the gas its ok. Pressing it abruptly causes the car to hiccup for a second or two and then it catches up. Repeated abrupt gas pedal movements result in same behavior.

While driving - it runs fine till it gets to operating temp. Few mins into operating temp, pressing the gas pedal to get upto speed (think of any acceleration scenario other than in a parking lot) and it stutters and stumbles. But it never dies out.

I can hear the fuel pump prime for 2 seconds or so with key in accessory. Fuel pump (purolator) and in-tank pump (Bosch) and filter/sock were changed about 2 years ago - probably in October 2012 That's about 12K-13K miles ago.

Always used brand name gas and never run gas below 1/4th tank except on a couple of occasions (never went into the red zone both times).

 

huh. The fuel pump should only run for 1-2 secs when you switch the key to RUN (II) not Accessory (I).

otherwise, I dunno. other than what you describe, the idle is stable at around 700rpm regardless of being in gear or park/neutral? if its cold, the idle might be more like 900, thats normal. when the engine is fully warmed up, unplugging the electrical connection to the idle air controller, and it should idle at about 500rpm (and probably not at all if its cold). plugging the idle controller back in should go back to idling about 700rpm... if all this is true, then your idle circuit is working fine.

 

I had the positions confused. Its on II as you mentioned - just went out and checked.

The car starts out at about 900 RPM cold and then comes down to around 780-810 range. Idle is smooth other than the shudder I described above during long crank starts. I have not tried unplugging idle controller. I had cleaned it in May 2013 since it was gunked up and was causing high idle after long drives. That problem is since gone.

 

Any thoughts on what else I could check?

 

the loose vacuum hose suggests maybe other hoses are cracked where you can't see them. Also, ANY air leaks after the AMM/MAF up to the intake manifold-to-head junction can cause erratic running.

your problem sounds a more than a little intermittent fuel starvation.

hey, did you check the crank position sender wiring? thats between the head and the firewall, stuck into the top of the transmission bell housing. if thats flakey, things run badly.

 

Do you have a picture of the CPS? I tried looking in the general vicinity of where you said and I cant seem to find (probably because I dont know what it looks like).

Thanks!

 

the problem is, its not in a location amendable to taking a decent photo

here's a diagram of what it looks like,


its literally directly behind the head, on the top of the bell housing of the transmission, right where the block meets the transmission.

 

Took a look at the CPS. It actually looks pretty good.

What next should I check in this never ending mystery? I still can't understand why the symptoms are so random and no CEL or code on the diagnostics port.

 

Reading back over your posts I came across these two items. The first - I'm not sure I understand. Was the hose running to the IAC shortened? If so, make sure there are no leaks. One hose from the IAC should loop down and then up through the intake manifold runners to a port on the top of the intake manifold. The other hose from the IAC should connect to the plastic air intake hose. If there are any leaks along this it could cause poor idle and running condition.

For the second item, make sure that the vacuum hose on the fuel pressure regulator is tight and does not leak. If the hose you have is not the right size, replace it with the correct one (sorry I don't remember the proper size). It should run to a nipple on the side of the throttle body.

 

Yes - that bottom hose from the IAC was shortened - about 0.5-1 inch I would say. Found it out when I cleaned it. It sits onto the IAc housing tightly. I can check it out again to make sure.

Also, the hose I am talking about seems to be the original one. The end that slides over the FPR connector/nozzle is loose and plugging/unplugging doesn't seem to change anything.

 

For both the idle air controller and the vacuum hose on the FPR, make sure there aren't any leaks. The IAC should have hose clamps on every connection except where it connects to the intake manifold. If someone shortened the hose, you might want to consider replacing it unless you are sure there are no air leaks.

I would go over the entire air intake system from the AMM to the throttle body making sure there are no leaks. Any un-metered air entering the system can cause all kinds of driveability issues and may not throw a code.

 

I have rechecked the resistance readings at ECU & ICU - numbers were same as before.

I have been keeping a log of temperature vs. starting hesitation. Keeping the car parked for 7 hours (after it has been warmed up with 20 mins of driving) everyday.
If the daytime temp is over 65F, then it has a delayed shaky start. Past few days temps have been in low 40s and it starts just great.
Starting the car after letting it sit overnight is never a problem.

Symptoms occur every time temp gauge is just under 1/4 on the gauge and gets worse as it gets to 1/2 point.

I have sprayed throttle body/air intake cleaner all over the engine and any hose/pipes and it never changed idle (done with cold engine as well as with engine at operating temp). I doused the air intake hose all the way from the air filter all the way to the throttle body in the hopes of finding an air leak - none. Idle never changed.

Edit: I did some more looking around on google. Other problem areas could be fuel injectors and/or the check valve at the fuel pump. How do I test either of these?
I tried driving it around for 20 mins (in addition to let it idle for 25 mins). I could not get it to stall. It just runs crappy - the more throttle I use, the crappier it runs.
Idle is always great - never shudders.

I am going to pour some fuel injector cleaner and see if it helps. Also going to replace that hose that runs from the FPR to the throttle body. Anyone knows what the part number is? I am going to get some generic hose from autozone and replace to see if it helps in any way.

The car seems to run really lean once its all warmed up.

What else remains to be checked other than giving up and taking it to a shop??

Edit: Fuel injectors and/or the check valve at fuel pump can also be suspect according to google. How do I check those?