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Hello, vehicle is a 2002 ZX3, 5spd, 97k.

I have recently been getting a P401 code but I do not think it relates to this issue, but I'm mentioning it because I could be wrong.

The other day I was driving home and noticed a sort of lag feeling when I let off the gas when cruising. When I got to my street I pushed in the clutch to coast and it immediately died. It would start if I pumped the gas and had to continue holding the throttle to keep it running. Drove it up the street fine with no coasting. No check engine light.

I did some research and found people mentioning DPFE, IAC, MAF, TPS, vacuum leaks, collapsed PCV hose among other things. I checked and sure enough the PCV hose was collapsed so I made a new one out of some fuel hose and a generic vacuum elbow from Autozone. Started right up, hit about 1300rpm and settled to about 800 or so like usual.

Yesterday I was driving and felt the same lag suddenly. Sure enough, same thing. Had to keep throttle input to stay running, fun to do in traffic with a 5spd. I continued to drive like nothing was wrong for another hour on the interstate to my friends house, then made the 2hr trip back home. Ran fine as long as I maintained throttle input.

Checked my replacement hose while running with a friend and it seemed fine. I tried replacing the DPFE, IAC, TPS, and cleaned the MAF. No change other than IAC. I tried each one at a time, since they made no difference I boxed them up and plan to return them. After replacing the IAC, if I could get it running pumping the gas, the idle would soar to 3000rpm then slowly settle down and then die, all without any throttle input minus what was needed to get it started. I put the original back on and am now back at square one.

I'm not sure what to make of the IAC. Possibly a bad one? Autozone is the only place I could get one on a Saturday afternoon so it's possible. If not, I'm on to fuel delivery. The fuel filter is about a year old. It doesn't seem like there is any easy way to diagnose a fuel delivery issue without a scanner. I have a pressure gauge, but no where to hook it up to.

Any ideas? I'm stumped and would hate to drop the tank and have no improvement! Thanks in advance.
 

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you will probably need to reset the ecu and let it re-learn the idle

and p0401 is a egr insufficient flow
p1401 is also egr pressure feedback high
p2401 is evap leak

since you just put p401 i put each number before it could be.
 

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Maybe you should take a closer look at the IAC; Run it longer, to give it plenty of time to learn idle. Several years ago, I had a similar experience with my '02 SE Zetec; I had to hold the throttle to keep it running, but it started & ran fine otherwise, & there were no codes. A new IAC fixed it.
 

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Maybe you should take a closer look at the IAC; Run it longer, to give it plenty of time to learn idle. Several years ago, I had a similar experience with my '02 SE Zetec; I had to hold the throttle to keep it running, but it started & ran fine otherwise, & there were no codes. A new IAC fixed it.
Did this because I suspected the same thing. It started out revving up to 3000rpm, then would slowly settle down and die. Each time it would rev up a little less, then settle down and die until it was back to hitting 1200rpm and instantly dieing.

Coil pack? PCV valve? Simple vacuum leak?
 

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Got a tee plumbed into my fuel line and checked the fuel pressure. About 33psi running and 50psi shut off. Sound about right?
 

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Did you unplug the negative battery terminal to reset the PCM after installing your new parts? Did you have to tilt the TPS to install it? If not, you probably installed it incorrectly.

Fuel pressure on this vehicle is tricky because it's constantly varying. That's why there's no port. The reason fuel pressure varies with this EFI design is because there's no return line. There is a procedure for checking fuel pressure, but yours seems like it's not the problem.

If resetting the PCM doesn't fix the problem, try unplugging the IAC to see if that makes a difference. If it does make a difference, clean your old one with carb cleaner, allow to dry, then install.

Check to be sure that all your air intake clamps are secure. From what I can read in this, it seems that you have more problems with vacuum. You might want to be sure that your PCV is doing it's job as well by blowing through the hose. If you want to remove it, the PCV acts as a one way valve. You should be able to blow through it from the engine side, but not from the vacuum side.
 

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Did you unplug the negative battery terminal to reset the PCM after installing your new parts? Did you have to tilt the TPS to install it? If not, you probably installed it incorrectly.
Yes.

If resetting the PCM doesn't fix the problem, try unplugging the IAC to see if that makes a difference. If it does make a difference, clean your old one with carb cleaner, allow to dry, then install.
Did not make any difference, plugged or unplugged.

Check to be sure that all your air intake clamps are secure. From what I can read in this, it seems that you have more problems with vacuum. You might want to be sure that your PCV is doing it's job as well by blowing through the hose. If you want to remove it, the PCV acts as a one way valve. You should be able to blow through it from the engine side, but not from the vacuum side.
Didn't blow through the hose, but the PCV rattled when I shook it making me think it's not clogged. Also, there was slight oil residue in the PCV hose on the intake end making me think the valve is working and hose is not clogged since the hose is brand new.
 

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Did not make any difference, plugged or unplugged.
Then something is either wrong with the IAC circuit, the IAC you purchased was bad, or is loose or leaking.
 
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