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420A Hesitation/rough idle

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609DSM

Proven Member
368
154
Aug 13, 2019
Langhorne, Pennsylvania
My idle is extremely rough when car is at temp. It goes from 950rpm and will drop down to 600 and as low as 500, does this when I come to a full stop at a light. Then it has trouble getting going, I have to really get on the gas to get the rpm to 1.5k to 2k for it to leave a stopped position.

I cant even go full throttle or what happens is it picks up speed then the torque just dropped and it revs a lot slower and gets a little quieter and all power it had comes to a halt, then randomly it kicks back in and has full power.

So I cleaned my intake and throttle body, replaced the MAP sensor and the throttle positioning sensor along with my broken coolant temp sensor. I've also checked for vacuum leaks as well and havent been able to find any from my inspections.

Could this be a fuel issue?
 
I have a new one but the tip is much shorter than the one that I already have in it. I was thinking of just switching it out and seeing just to try it but havent yet
The tips just unscrew. Unscrew the tip from the old one and put it in the new one. Just be sure you measure the length before doing so or you could take that thing out 15 times to adjust it right. I have spent the last couple of days doing so myself...
 
Okay I'll have to check this out. I tried fiddling around with it but the only movable part I found was the sleeve of the tip
It is on there pretty tight. I covered it with a towel to keep it from scratching and twisted it off with some pliers. Once you break it loose it should unscrew easily. Just be careful not to damage the tip, hence the towel.
 
Took me like 20 tries to get the car started. Doing the idle relearn now. Running for 5 minutes, shutting off. Nice easy drive for 20 minutes then shutting off
It's odd that it wouldn't start. I've started the car without an IAC at all. Let me know how that process goes and the results.
 
The only one I haven't checked is evap, I believe that is what it is. The one on the top by the throttle body. I do have a large evap leak code. I'm thinking I can just cap off that port and see if that helps? I have no idea where that line is leaking at
 
The only one I haven't checked is evap, I believe that is what it is. The one on the top by the throttle body. I do have a large evap leak code. I'm thinking I can just cap off that port and see if that helps? I have no idea where that line is leaking at
Try just putting a vacuum cap on the port and then starting the car to see if it helps.
 
I have no idea where that line is leaking at
Neither did I. That's why I deleted the system. It is nearly impossible to find a small leak in all this mess:

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I have. No idea where this leak is coming from but I hear it behind the intake mani
Did you use a gasket or some sealant when you put the egr blockoff plate on the rear of the intake mani? if not, it is leaking.
 
Yes but the threading is stripped on the bottom bolt, I dont hear it or feel it leaking. Tried blowing smoke around and didnt see anything being sucked up
Does your car have cruise control? If so, check that little black reservoir that sits under the upper intake manifold. Mine was cracked and leaking vacuum. You can delete that by running the hose straight from the intake mani to the cruise control servo.
 
Checked my vac lines from the mani, looks like it's the FPR vac line that has hardened and is splitting. Going to buy a new line today and replace it, see if that fixes my issue. Starting to make sense that is the source of the issue since it is responsible for monitoring my fuel pressure
 
So after seeing which vacuum line was the issue by unplugging one at a time and putting my finger on the port to see how it effected the engine, to my surprise it had no effect. It sounds as though the vacuum leak is from the egr port (the bottom threading has been really hard to get the bolt into since I started tinkering around).

After doing all that I went to drive my car home and it was running surprisingly well, had full power and felt like a new car! I was confused though, didnt know what was going on. Soon after it just took a dump, when I came to a stoplight it wanted to stall out and was idling extremely rough and sounded like the exhaust was leaking.

Not sure where I'm gonna go from here, cant realistixly drive it around...
 
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