STFT at +25 and LTFT at -25 when at idle?! *Solved but I wanna cry

Summary for what's been worked on in the engine bay.

Previous Owner
Installed Short Ram CAI
New Radiator (I believe aftermarket but will check later if OEM)
JANKY aftermarket exhaust (If you saw the welds on this thing you would throw up)

Fuel Injectors
Fuel Pump Relay
New VTCS solenoid
New VICS solenoid
New Spark Plugs
New Coil Packs w/ wires

MAF Sensor
CAI Filter
EGR Valve
IAC Valve
Throttle Body
Intake Manifold

Check Engine Light Codes
P0660 - Secondary Shutter Valve Open
P2009 - Intake Manifold Runner Control Circuit Low Bank 1

NO P0171 so no vac leaks, I even still doubted and sprayed around intake manifold for any leaks but no changes.

So to not summarize this time at idle STFT is at +25 and LTFT at -25 at idle, car was driving fine for a couple hours some rough idle issues but progressively got worse throughout the night. Had a feeling it was my fuel pressure sensor as when I disconnected it from the solenoid car ran the same exact way. Tested the solenoid with some jumper wires and clicks fine. Vacuum flows correctly so not that, no hole in the lines either. The craziest part about all of this is that when I step on the gas or drive it is smooth sailing. If I feather the gas (In park) the STFT stays between -5 and +5, LTFT stays at +4. When actually driven readings are also normal. Along with this I watched my O2 sensor voltage at idle. O2 sensor 1 - 0.07v. O2 sensor 2 - 0.04v and same freakin thing with the car at least getting gassed reading will go back to normal such as each sensor reading between +0.10v and 1.00v while rapidly changing. After seeing the rough idle I had the car turned off and turned back on, RPMS will go between 100 (Sounds like I have big ass cams installed) and 1100 RPMS for about 5 second and then ROUGH idle at 650 RPMS. Give it 15 seconds and it'll start the whole process over again with jumping and rough idling. I noticed I also have an issue with my fuel pump not starting the pressurization process with the key in the ON position (Just silence even with the seat pulled up and metal cover taken off) , pump will turn on with Ignition so car always starts. I even tested the pump with jumper wires in the engine bay and pump activated perfectly. The car actually runs better the less it idles and what I mean by that is if I drive around without stopping the idle is less rough and usually doesn't get rougher (EX: RPMS dropping or building) it sits pretty well.

My guesses for what's wrong are:
Faulty Fuel Pump
Faulty Fuel Pump Wires
Hole in exhaust manifold
Faulty CAT

I love the hell outta this car and can't figure what's wrong with it this time. If any experts and/or enthusiasts can help out with any guesses it would greatly be appreciated.


The Diagram Dude
2002 MP5
One last thing I can think of is your intake tube.
I don't even know if the intake tube is used with your CAI, but on my car it involved the STFT and the LTFT, so it might be something to look at.
It was 10 years ago, so my memory is a bit foggy.

OH MY GOD, so I might have just found the issue. So during my look around of my CAI just nit picking it was look really good so it just had me dumbfounded. I was hearing a gurgling noise underneath the end bbn of the CAI which was confusing the HELL outta me cause it would be there and gone sometimes. My metal EGR Pipe, ya know that super difficult one that connects from the beginning exhaust manifold and comes back to the bottom intake manifold. Well yea the bolt isn't connected 🙃 I did my best with trying to tighten it back on and only got the bolt half way before it required the strength of a thousand silver back gorillas. So rn it's too dark to disassemble my throttle body to have better access to it so tmr morning is gonna be fun. When I tightened it half way when i turned the car back on P2009 and P0660 completely went away. I'm sure there is still air leaking through the bolt connection as I'm still having issues at idle atm but I'm sure once it's flush we'll be a lot better. Probably wouldn't have found it if I didn't take off the CAI to inspect it lol. Will give an update tmr afternoon
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So update on issues, EGR pipe was causing the codes but NOT the idle issues. The EGR pipe was loose enough to where my brain couldn't comprehend what's happening with the car but at this point after tightening it back on. Still have idle issue, I have to pin point it this time to old AF fuel pump. The reason why is because after resetting the car driving it around it felt nice, had some issues when coming to a stop but it was in the learning process. After driving around for a while car feels nice, I get ready for the gym and take a shower let the car sit for about 30 min. I get back in
1. Rough start
2. Rough idle
3. Idle jumping
4. Idle fixes itself after 5 min of going back and forth

I believe it's the fuel pump as when I watch the STFT and LTFT + watch both O2 sensors.

I was not getting enough fuel at all, sitting at -12 and gets worse the lower the idle goes and both 02 sensors will read way too much air due to the car not having enough fuel the O2 sensors are fighting to keep the car alive while the pump is going crazy. Either it's an electrical connection with the pump or the pump itself. My pump does not prime with the ignition key in the ON position so I'm having fuel issues and no air leaks atm. I will try to order a new pump and give another update in about a week to 2 weeks time

Some more details as to why I believe it's the fuel pump, car sputters and I actually hear an audible vacuum coming from the rear when taking off from a stop. Since I have a giant exhaust in the back, this time when it fights I hear gurgling noises from where the fuel pump is located as if it can't do it's job. When I step on the pedal the noises and resistance along with how the car is accelerating from a stop are all very closely related. When the sputters stop I have more control over my gas.
Last edited:


The Diagram Dude
2002 MP5
You should consider replacing the fuel filter while you're in there.
A clogged fuel filter can cause fuel pressure issues and strain the fuel pump.


You should consider replacing the fuel filter while you're in there.
A clogged fuel filter can cause fuel pressure issues and strain the fuel pump.

View attachment 317706

So I had a question about this. My car ran great for 3 or 4 days. Then went back to it's idle issues. So I do believe the filter is clogged and is straining the pump itself. I was curious to ask about the housing. So I understand after disassembling the fuel pump that the strainer is the filter, is there also a filter with the housing itself? Or is it just the filter screen itself as the only filter? Also as another note, seeing if it is just the screen as the only filter between the gas tank and engine. I may install a K&N Fuel Filter on the fuel line before the rail.

Update on how the car is, with it being strained after around 2 or 3 hours of driving when the idle issues happen. They will dirty the HELL outta your spark plugs. Yesterday I started to have misfires when these are new spark plugs. Pulled them, cleaned them with a wire brush very very softly to take off the carbon. No more misfires, just be mindful that the low idles will ruin your plugs very fast.
So after driving my car around for almost 2 weeks with the new fuel pump housing and fuel pump. My filter was definitely clogged and absolutely killed my last pump but over time I realized that this is simply what was causing my consistent low idle but not my drop in random idle. With the new "fuel system" (ofc not the whole thing) components replaced I have had a consistent idle of around 750 to 800 which is better than my usual before hand. I still have had a drop in idle and can probably pin point it rn... maybe.

So my car doesn't stall and at a stop I have a steady idle that will then drop occasionally, after driving around I heard a very loud ticking noise from the engine. Mind you I have an aftermarket exhaust and I heard it clear as the morning birds through the cabin. Popped the hood and it's my EVAP solenoid. I believe this is the culprit as I did replace this component this was one of the first items I accidentally broke when I first got the car. Didn't know about rockauto at the time and decided to go cheap through Amazon. Them china parts ain't reliable. My second guess as to why it's this part is due to the audio similarities. So when I have my normal idle and the car is as smooth as butter. It's ticking is very low and I can't hear it over my engine but when the engine drops and gets rough the ticking gets louder and higher pitched from the solenoid. Then it'll just randomly work again with me barely able to hear it, it's very strange that it's happening this way but my car still runs without any issues besides that. It hasn't gotten worse or caused any major issues with the car but I believe it's a faulty part from me just being cheap.
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Also tested something out with the solenoid rn I unplugged it while my car was running and I still have an issue of the idle dropping but with the solenoid disconnected my idle increased to 800 and 850. I just wanna get rid of that random idle drop
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Okay I know that I've been away from this post but I found the reason as to why I was having idle drop. It was my Alternator!?!? After some time of just doing regular maintenance and cleaning it inside and out. Over time I had a bearing from one of my pulleys that made my car sound like rocks. Most people said it could be the alternator bearing as that was the most common for them but while getting the belt off my my Alternator and Water Pump. My Alternator bearing is fine but the Alternator itself is covered in grease from the CV Axle boot the was popped and dirt dry before I bought the car. It's one of the first things I replaced. (This is my first car and wasn't ready for doing things myself but honestly wished I did it myself). Since it was covered in grease I still decided to take it to Autozone to get it tested and fails. It fails and give only 11.8V. It runs at normal 14V after ignition but is once in a blue moon giving me false CEL codes. Like a radiator fan that for some reason isn't working even though I'm watching it run with my own eyes. So this is to solve the issue with my idle drop but that bearing.... yea. Gotta fix my water pump and I wanna cry... anyways thx everyone for all the help and info it's finally solved to have a solid idle.

TLDR: I have a jacked up car and replaced like 60% of it to get it working without any issues for idle problems :)