2G stuck in limp mode

tschuhly · Jul 1, 2026

Hey all,

I am trying to figure out what steps I should go through to figure out what is causing my issue.

Some background is that the car has been put together and running since about mid April. Towards the middle or end of May it started to act like it had a misfire or something. I replaced the spark plugs with the higher horsepower ones but that didn't do anything.

I decided to check for codes and I got the knock detection circuit fault code. I found that my sensor was loose so I tightened it up and no luck. I then was driving it and as I took off from a light, it sputtered a little and when I gave it slightly more gas it bucked hard once and then turned off. I got it towed and later found that my ECU 20amp fuse had "blown" or broke (I'm not sure if it was just old and brittle or if it legit blew). I replaced it and my knock sensor with a new one jic and my car started up except now it won't go over 4500rpms.

It doesn't have any codes but is still running a little weird and is still in limp mode. I tried to go into my ECU pinout settings to tamper with them to see if it was because of my AEM boost sensor being pinned to my MDP pin, but it is still in limp. I will say that for a little bit I had forgot to unplug my stock MDP so there were probably 2 conflicting signals going to the ECU so maybe that did something? I haven't driven it yet because I worried it will leave me stranded again.

I attached a log of it starting, idling and revving a little. Any guidance would be appreciated!

99dsmer4g63 · Jul 30, 2026

The plastic cap with the black wire and “shield” wire are factory. There is a few ground connections like this buried in the harness in the nearby area.

Sheridan Engineering Products

STM carries Sheridan Engineering products - all those hard to find sensor connectors and harnesses for Mitsubishi Evo, DSM, 3000GT and more. If you don't see it online yet, just give us a shout!

stmtuned.com

-Daniel

tschuhly · Jul 30, 2026

Also, I called a local Mitsu dealer and the parts guy gave me to seemingly useful links for terminals and connectors that I will put here for helping future people.

Automotive Connectors | Connector Experts

Looking for the best automotive connectors on the market? Connector Experts has an expansive collection of products. Shop for top-quality connectors.

connectorexperts.com

Shop Automotive Connectors

Discover a wide range of automotive connectors, pigtails, and plugs at findpigtails.com. Lightning-fast search, helpful tools, and how-to repair guides available. Trusted by dealerships and insurance.

findpigtails.com

tschuhly · Jul 30, 2026

99dsmer4g63 said:
The plastic cap with the black wire and “shield” wire are factory. There is a few ground connections like this buried in the harness in the nearby area.

Sheridan Engineering Products
STM carries Sheridan Engineering products - all those hard to find sensor connectors and harnesses for Mitsubishi Evo, DSM, 3000GT and more. If you don't see it online yet, just give us a shout!
stmtuned.com

-Daniel

Do you think I should reroute an entire new wire from the ECU to the sensor? If so, what's the best way of doing this in your experience or is there anything to keep in mind? For instance, this is definitely a different wire than the rest, do you know what I should purchase if going this route?

I think I may also try to run a wire from the sensor to the ECU temporarily just to see if it makes the rough idle and throttle go away to see if this truly was the issue.

tschuhly · Jul 30, 2026

Final update...I think I've most certainly found the problem.
The wire on the harness side of the knock sensor plug, was apparently damaged enough to not be making a good connection with the plug pin but it hadn't pulled out of the connector completely which is why I didn't see it. I am going to attempt to repin that to see if that fixes things!

steve · Jul 30, 2026

That would be great if that was the only issue.

The wire from the knock sensor is much like a shielded microphone cable. The inner conductor carries the signal and the outer braid is a noise shield and is grounded the the ECU end.

tschuhly · Jul 30, 2026

I was so sure that that was the issue but alas...it is still a giant, way too expensive paperweight.

Steve, I know you said you wouldn't drive it. I just drove it for a couple of minutes to see if the knock sensor code would come back, which it didn't. The thing it, it still feels exactly the same... My plan now is to drive up to the tuner to see what he thinks since that seems to be the only other thing that could be going on here.

You must be logged in to view this image or video.

1990TSIAWDTALON · Jul 30, 2026

Could the knock sensor be holding it back if its bad, maybe. Crossing fingers for good luck

tschuhly · Jul 30, 2026

I replaced it with one that came with the car as a spare (the car came with multiple of things including engines and transmissions) and then when that didn't work, I went ahead and replaced it with one of these: https://www.extremepsi.com/OEM-Knock-Sensor-Mitsubishi-Lancer-EVO-VIII-and-IX.html

I did read somewhere that torque spec on these sensors is extremely important, but I can't imagine that I over torqued it. Maybe I need to double check that it hasn't loosened back up, but other than that I am at a loss.

jdxnc · Jul 30, 2026

It sounds like it's breaking up but my bigger concern would be your oil pressure gauge is very low and the the dummy light is flashing.

tschuhly · Jul 30, 2026

jdxnc said:
It sounds like it's breaking up but my bigger concern would be your oil pressure gauge is very low and the the dummy light is flashing.

I am pretty sure the stock oil pressure gauge is because I have a splitter off of the OFH and I may have reversed the OEM sender and dummy light sensor locations/wires. I have just been using my aftermarket which is the mechanical gauge at the top of the pillar, and it typically reads around 15 or 20 psi at idle when warm which I heard is fine. I am planning on fixing that once I get this sorted out. Good call though!

1990TSIAWDTALON · Jul 30, 2026

when my dummy light comes on, I shut down IMMEDIATELY. I had an oil filter come loose A LONG TIME AGO and that saved me (I have a big hose clamp on it now). I also QUIT DRIVING my nice stock 90 GSX because that light was flickering at idle. I don't ever want to hurt the motor so I haven't driven it in over a year, but have a brand new rebuild ready to go in, when I can schedule that. :thumb:

tschuhly · Jul 31, 2026

1990TSIAWDTALON said:
when my dummy light comes on, I shut down IMMEDIATELY. I had an oil filter come loose A LONG TIME AGO and that saved me (I have a big hose clamp on it now). I also QUIT DRIVING my nice stock 90 GSX because that light was flickering at idle. I don't ever want to hurt the motor so I haven't driven it in over a year, but have a brand new rebuild ready to go in, when I can schedule that.

Maybe while I am trying to figure out the current issue, Ill go ahead and fix the oil sensor setup to see if it causes all of the to go out!

tschuhly · Aug 4, 2026

Alright, still haven't heard from my tuner so I have been looking into stuff myself and want the experts opinion to see if I am thinking correctly.

As Steve pointed out prior my ISC is at 90, so I adjusted that down to 40ish (I have 272 cams). I then clamped off my FIAV and found that my ISC then dropped to 20 but my idle didn't change at all. Could this point to the famous "hidden vacuum leak" when the FIAV is stuck open that would cause this stuff?

I want to get some confirmation before I go ahead and tear it all apart.

dwb · Aug 4, 2026

More than likely your FIAV was at least partially stuck open. Did you still have coolant lines hooked up to the TB? Now that you closed off the FIAV, you will want to loop or cap those lines.

tschuhly · Aug 4, 2026

dwb said:
More than likely your FIAV was at least partially stuck open. Did you still have coolant lines hooked up to the TB? Now that you closed off the FIAV, you will want to loop or cap those lines.

I did have the coolant lines. As far as I have researched, I will want to tighten the FIAV spring all the way down, cap off the coolant line on the FIAV side of things and then loop the coolant line from the therm housing down to the heater pipe. Ill finish up in a sec and report back!

dwb · Aug 4, 2026

tschuhly said:
I did have the coolant lines. As far as I have researched, I will want to tighten the FIAV spring all the way down, cap off the coolant line on the FIAV side of things and then loop the coolant line from the therm housing down to the heater pipe. Ill finish up in a sec and report back!

That's exactly what I did! :thumb:

tschuhly · Aug 4, 2026

Alright, well it seems like it is running better but still not 100%. Could it be a combo of my FIAV and IAC? I may tackle that next. I also noticed that my car was tuned while this was clearly bad since the ISC position was at 88 in the tune log. Would I need to get it retuned now that I fixed this and adjusted it down to the correct ISC position?

Also, I think I found what blew my fuse the first time. I just tried to plug my MDP back in without unplugging my 3.5 bar AEM sensor and it almost immediately went. If I am not currently running SD, should I be using my MDP or my aftermarket boost sensor? Would I have to do anything different than the typical aftermarket boost sensor setup in the ECU inputs tab in ECMLink v3?

tschuhly · Aug 4, 2026

Update number 30725: I went and got two new fuses and as soon as I turned the key for both of them, they blew. I have no idea what's now all of the sudden causing this since I've since unplugged my after market AEM boost sensor. This ride from hell conveniently waited again until I had already driven about a mile away from my house but as far as I'm concerned, this piece of crap is about to wind up on bring a trailer...

steve · Aug 4, 2026

I did a not so quick pass over what's been discussed and I didn't see anything about blowing fuses before today so let's start with which fuses are blowing when you turn the car on. Also since there are several positions to the ignition switch are we talking about the accessory position, the engine on position, or the engine start position. Each adds to the circuit's being powered.

tschuhly · Aug 4, 2026

It's all good Steve! There is certainly a lot in this journey and the fuse hasn't really been a main issue up until this point.

Just to circle back around, when my car initially shut off the first time (a month or so ago) it would crank but not start. I found that the main engine/ECU fuse (20amp big blue) had blown. At the time I thought maybe the jerk of the car just broke it since it was very old and weathered. This is the first time since then that it has happened again.

I am unsure when it blows but my plan is to go over and do a step by step process to see when exactly it blows. My plan is unplug a ton of the sensors, put new fuse in, click to ACC, Click to ON, then plug sensors back in one by one until it blows again.

Does this sound like the right process?

I had a local guy tell me that he has heard that the fuel injector harness is a weak point for this and also he has seen the ISC short out internally and cause this. I'm suspecting it's that.

EDIT: Alright, so I unplugged all injectors, MAF, IAC, knock, ptu, and MDP. When I clicked to ACC, the fuse stayed, clicking to On blew the fuse.

steve · Aug 4, 2026

Interesting

tschuhly said:
I found that the main engine/ECU fuse (20amp big blue) had blown.

...

EDIT: Alright, so I unplugged all injectors, MAF, IAC, knock, ptu, and MDP. When I clicked to ACC, the fuse stayed, clicking to On blew the fuse.

Interesting. The main 20A fuse (Fusible Link #4) feeds the MPI circuit but the Ignition Switch is fed from the the 30A Fuse (Fusible Link #6). Turning the key to the ON position doesn't seem to be popping the 30A so it's something the IG1 or IG2 but not ACC. IG1 causes the ECU to activate MPI circuit and that powers the MAF, cam and crank sensors, the O2 heaters, BSC, FPS, EGR, ISC, and Injector resistor. The MDP isn't on the MPI 12v feed, it's on the 5v sensor power. The PTU is powered from the 30A Ignition fuse along with the coils, fuel pump, etc but again since the 30A isn't popping it's not any of those.

You must be logged in to view this image or video.

tschuhly · Aug 5, 2026

So I went ahead and keyed the car on after unplugging all sensors. Plugged them in one by one and nothing blew it. I did notice that the 3rd plug from the top of the ECU made some odd noise (possibly shorting) when I plugged it in without first plugging in the big bottom plug. Went to drive it home and it did the hard bucking thing a couple of times which made the engine light kick on. Almost got home and it gave one final buck and shut off. The fuse blew again... I decided to do the test again and found that the 3rd plug from the top on the ECU (the bigger of the smaller middle plugs) blew the fuse.

I opened the ECU up again and aside from things looking like an older ECU, I don't see anything obvious. Though, I don't really know what I am looking for. My plan now I think is to see what is connected to that plug and trace that. Worst case scenario, I head down to ECMTuned since I am in Southern PA and they are in Frederick MD I believe.

Just did a continuity test on the plug and now I am sweating bullets with how many pins are hitting when testing for continuity to ground...unless these are the ground wires for sensors and stuff. Does this mean that I need to chase all of these wires? Would this kind of point to a spot in the harness that has melted these wires together?

I am not sure what the next step would be here diagnostically.

You must be logged in to view this image or video.

dwb · Aug 5, 2026

Was it this thread where the OP found a mouse? And now all of a sudden you're tripping fuses? Seems too coincidental.

tschuhly · Aug 5, 2026

That was this one, but I actually tripped a fuse at the very beginning of this whole journey after getting the car tuned and daily driving it for about a month. It may be important for me to point out that I also was the one that asked for help with testing my fuel pump using the plug in the harness. I found out that instead of applying power to the fuel pump test plug, I had accidentally applied the power to the blue, Engine speed plug. I didn't think that this had caused any issues when the car seemed to run fine initially but now, I am curious if that is coming back around to bite me.

OR...it's that freaking mouse...

With key off:

-I have constant 12v to MPI relay wire.
-I have .822 show up during continuity check with no beep on power steering switch wire.
-i have .018 show up with beep during continuity check on engine light wire.

I will note that my white alternator wire showed ground continuity yesterday right after this happened and now it doesn't which seems odd to me.

I also checked my MPI fuses visually and see no burns, then functionally and they are functioning

Is this all normal? Is this how I should check it?

tschuhly · Aug 6, 2026

I also thought that I posted the video of my plugging the wire back in but must not have. This is my testing for a popped fuse yesterday. Everything is plugged in at this point except the plugs that you can see and as you can hear, the key is on.

You must be logged in to view this image or video.

The Central Hub for DSM Community and Information

2G stuck in limp mode

tschuhly

Attachments

99dsmer4g63

Sheridan Engineering Products

tschuhly

Automotive Connectors | Connector Experts

Shop Automotive Connectors

tschuhly

Sheridan Engineering Products

tschuhly

steve

tschuhly

1990TSIAWDTALON

tschuhly

jdxnc

tschuhly

1990TSIAWDTALON

tschuhly

tschuhly

dwb

tschuhly

dwb

tschuhly

tschuhly

steve

tschuhly

steve

Attachments

tschuhly

dwb

tschuhly

tschuhly

Similar threads

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds