Need intake help

[Jim's new TJ]

Hey gang.
I'm new here and to "forums" in general.
Last Jeep I owned was an '83 CJ7, 258 I6, 2bl, but had to get rid of it before the internet even existed so I'm not sure how this all works but I need help!
Just got my hands on a 2000 2.5l TJ. But, it came with some previous owner mods/issues. He said he put a throttle body from a 4.0 on it and bored out the manifold. It's also got a spacer plate +- 1". It Idled REALLY high- I'm talking about coasting with the clutch in, through the Wal-mart parking lot at 4200 RPM!
I have the original 2.5l TB and have swapped it back and forth using the MAP, IAC, and TPS from both TB units in many different combinations. Things change with different combos- hard start/low or no idle, but nothing is even close to a fix.
On it now is the 4.0 TB and spacer. I've got 4 OBD codes:
P0-0505,
0135
0171
0121
Any ideas where to start?
All help is appreciated

 

[Chris]

Hey gang.
I'm new here and to "forums" in general.
Last Jeep I owned was an '83 CJ7, 258 I6, 2bl, but had to get rid of it before the internet even existed so I'm not sure how this all works but I need help!
Just got my hands on a 2000 2.5l TJ. But, it came with some previous owner mods/issues. He said he put a throttle body from a 4.0 on it and bored out the manifold. It's also got a spacer plate +- 1". It Idled REALLY high- I'm talking about coasting with the clutch in, through the Wal-mart parking lot at 4200 RPM!
I have the original 2.5l TB and have swapped it back and forth using the MAP, IAC, and TPS from both TB units in many different combinations. Things change with different combos- hard start/low or no idle, but nothing is even close to a fix.
On it now is the 4.0 TB and spacer. I've got 4 OBD codes:
P0-0505,
0135
0171
0121
Any ideas where to start?
All help is appreciated

Starting with your high idle issue, it seems like the throttle body swap and modifications could definitely be contributing to the problem. A few things to check:

Throttle Body Alignment: Make sure that the throttle body is properly aligned and that there are no vacuum leaks around the gaskets. Even small leaks can cause high idle issues.

IAC Valve: Since you've tinkered with different throttle bodies, the Idle Air Control (IAC) valve might be acting up. If it’s not calibrated correctly for your setup, it could be causing the high idle as well. Cleaning or replacing it could be a good step.

TPS Sensor: Make sure the Throttle Position Sensor (TPS) is functioning properly and calibrated. Sometimes, when swapping components, it can get out of adjustment, leading to erratic idle behavior.

Vacuum Leaks: Inspect all vacuum hoses and connections thoroughly. A vacuum leak can present a host of issues, especially with modified setups like yours.

As for your OBD codes:

P0505: This code indicates a problem with the idle control system. This is likely tied to your high idle issue. It could be the IAC or a vacuum leak.
P0135: This points to an issue with the O2 sensor heater circuit (upstream). Check the wiring and connections of your O2 sensor.
P0171: This usually indicates a lean condition. This could be a result of either a vacuum leak or an issue with your fuel system.
P0121: This is linked to the TPS. If you haven’t already, consider replacing it if you suspect it isn’t working correctly.

Good luck, and keep us updated on your progress!

 

[Jim's new TJ]

Starting with your high idle issue, it seems like the throttle body swap and modifications could definitely be contributing to the problem. A few things to check:

Throttle Body Alignment: Make sure that the throttle body is properly aligned and that there are no vacuum leaks around the gaskets. Even small leaks can cause high idle issues.

IAC Valve: Since you've tinkered with different throttle bodies, the Idle Air Control (IAC) valve might be acting up. If it’s not calibrated correctly for your setup, it could be causing the high idle as well. Cleaning or replacing it could be a good step.

TPS Sensor: Make sure the Throttle Position Sensor (TPS) is functioning properly and calibrated. Sometimes, when swapping components, it can get out of adjustment, leading to erratic idle behavior.

Vacuum Leaks: Inspect all vacuum hoses and connections thoroughly. A vacuum leak can present a host of issues, especially with modified setups like yours.

As for your OBD codes:

P0505: This code indicates a problem with the idle control system. This is likely tied to your high idle issue. It could be the IAC or a vacuum leak.
P0135: This points to an issue with the O2 sensor heater circuit (upstream). Check the wiring and connections of your O2 sensor.
P0171: This usually indicates a lean condition. This could be a result of either a vacuum leak or an issue with your fuel system.
P0121: This is linked to the TPS. If you haven’t already, consider replacing it if you suspect it isn’t working correctly.

Good luck, and keep us updated on your progress!

Thanks for the feedback. I'll swap all gaskets and replace/verify all sensors etc. and follow your lead.
Is it possible I need to switch back to an OEM 2.5l manifold or should I be able to resolve this with what I have now?

 

[macleanflood]

I'd get back to stock ASAP.

A smoke tester will show you all your leaks. I'd start there.

-Mac

 

[Chris]

I'd get back to stock ASAP.

A smoke tester will show you all your leaks. I'd start there.

-Mac

^this

 

[ItchyDong]

For god sake. Go back stock. What a nightmare.

 

[SSTJ]

Thanks for the feedback. I'll swap all gaskets and replace/verify all sensors etc. and follow your lead.
Is it possible I need to switch back to an OEM 2.5l manifold or should I be able to resolve this with what I have now?

Welcome to the forum.

If it can fit right without leaking, I suppose that being bored out won't hurt anything. (Nor help anything.) But you may end up removing both manifolds just to re-set everything and ensure a good fit. If so, you might want to go back to stock while you're at it.

If it's helpful, I recently replaced my 2.5 manifold and my notes are here.