New ECU now high idle and terrible surge

[AliceCooper]

So I replaced the ECU in my car which fixed the no starting issue. Now it idles around 2100rpm and begins to surge after about 15 seconds of run time. My car surged before but it is even worse now. The BISS screw will not change the idle RPMs at all. Also my ECU was clicking when the doors were closed and the battery was really low. I would like to know why my BISS wont change my idle and why my ECU was clicking. Also when driving around, when i go to switch gears and put the clutch in the RPM will go up by like 100rpm for a second then drop. It feels like the throttle is sticking but what would all of the sudden cause this?

 

[donniekak]

First off, your biss not changing the idle is a huge vacuum leak somewhere. Second, your ecu is not clicking, its probably the mpi relay. Does the ecu have new caps?

 

[AliceCooper]

First off, your biss not changing the idle is a huge vacuum leak somewhere. Second, your ecu is not clicking, its probably the mpi relay. Does the ecu have new caps?

So could my BISS be that vacuum leak? I know i tested some hoses for leaks from the Purge Control Solenoid Valve and the one next to it and they checked out. Yes this is a new ECU.

 

[donniekak]

Break out the boost leak tester and spray bottle of soapy water. New ecu, as in its in a silver case?

 

[AliceCooper]

Break out the boost leak tester and spray bottle of soapy water. New ecu, as in its in a silver case?

No i think it is a rebuilt one or something. Ok so ill spray that onto the BISS and see if it leaks?

 

[donniekak]

Pressurize the entire system and spray the soapy water on all connections starting from the turbo to the injectors, look for bubbles.

 

[flinguist]

The vacuum leak problem you have may have destroyed your ECU in the first place. If the ISC is being over driven by the ECU because of a vacuum leak the ECU can be damaged. Another possibility is a bad ISC, which could cause idle problems, and damage your ECU. driver01 [ECMTuning - wiki]

 

[AliceCooper]

Ok guys I now also ontop of that stuff above, something is shorting out behind the dash causing my battery to drain over night. I'm thinking whatever is making that clicking is the culprit or could a bad ECU cause this along with these other problems? Because these problems appeared out of nowhere after putting in this new ECU after it has been sitting in my garage waiting to get running again.

 

[steve]

Just because it's "new" doesn't mean the ECU is good.

 

[jeffo]

My thoughts exactly. Sounds like another typical "rebuild".
Is the new ECU a 1990, or is it the proper 1991-94 ECU? Mitsubishi switched the Idle Position Switch wire between 1990 and 1991, and using the wrong ECU will cause idle surge issues if you don't swap the wires.

 

[AliceCooper]

My thoughts exactly. Sounds like another typical "rebuild".
Is the new ECU a 1990, or is it the proper 1991-94 ECU? Mitsubishi switched the Idle Position Switch wire between 1990 and 1991, and using the wrong ECU will cause idle surge issues if you don't swap the wires.

Hmm I didn't know that. I did not buy the ECU either my dad bought it. We think this ECU is whats causing a lot of problems with my car because now we think all of the sudden there's a short somewhere in my car. Guess i just have to wait for my EPROM one to arrive. I'll update when i get the new ECU installed. Also, could a bad ECU cause boosting problems? All of the cuplers on my piping are clamped down tight and when i boost my car starts jolting like its leaking hardcore boost or something. This also started after it had been garaged for 4 days without use.

 

[AliceCooper]

Ok guys, I am not sure about the year the ECU that is currently in my car is for, BUT it is drawing around 3.5amps from my car while everything is completely turned off. We unplugged the center plug from the ECU and only .01amps was being drawn from my battery which is next to nothing. I check my IAC motor and it proves to be good with 40 ohm resistance for all the pairs of pins you test. I am thinking this ECU is what is causing all of my problems. Let me know what you guys think, I have an EPROM ECU showing up either tomorrow or saturday.

 

[jeffo]

Sounds bad to me. The ECU should only draw a few milliamps to keep the memory alive when the car is turned off.

 

[steve]

Sounds like your ECU isn't turning the MPI relay off.

The ECU itself only draws a couple hundred milliamps when running, it's all the rest of the sensors and solenoids on the MPI circuit that draw current.

When you pulled the center plug, you disconnected the MPI relay control signal and that turned the MPI relay off.

 

[AliceCooper]

Sounds like your ECU isn't turning the MPI relay off.

The ECU itself only draws a couple hundred milliamps when running, it's all the rest of the sensors and solenoids on the MPI circuit that draw current.

When you pulled the center plug, you disconnected the MPI relay control signal and that turned the MPI relay off.

Ok yeah my new one is arriving soon so we will see. Also my buddy thinks my surge problem is coming from my TPS. Can i test that with an ohm meter like my IAC motor?