2002 SSV Supra - High Idle - WOT Bogging down

I've been helping my brother with his boat he bought last year (750 hrs). We've replaced everything the previous owner failed to do, got it cleaned up, and have almost everything working. The boat has a 350 Indmar Assualt TBI.

We are still having two major issues that I can not figure out.

First is a high idle. It cranks up an runs at 800, then after putting it in gear and driving for a bit, it stays at 1000-1100. I have yet to verify the throttle cable isn't sticking by pulling it off, but it is always resting on the stop so I don't think this is the issue. The engine needed a new IACV when he purchased it, so we replaced the IACV and TPS with one from an LT1 corvette from a parts store rather than Indmar. I also suspect this could be the issue, but doubtful with my experience in GM parts. I am going to get the parts we pulled from it, and verify the IACV is the same length. Yesterday, we also tried to swap it out with a MAP sensor I had laying around with matching P/N. No change. The only gasket/hose we have not replaced is the intake manifold to the head. Spraying carb cleaner around it doesn't change the RPMs. TBI gasket, TBI adapter plate gasket, PCV hose, CTS,& MAP hose all replaced. Flame arrestor was cleaned as well. We have hooked a laptop scanner to it my buddy had and all parameters seemed to be within reason. Where should I look next? I'm running out of ideas and I'm am very familiar with GM engines and EFI tuning.

The other issue is if you're idling and slam WOT, it bogs down and will die. I need to check the base timing. I also need to verify fuel pressure which I read was supposed to be over 40psi. Is there a screen in the tank on these boats that could possibly be clogged? It runs fine other than slamming WOT. Also starts with no issues.

Other than that, my last place to check is a compression test but that wouldn't cause the problems from my experience. I know it doesn't take much to make the TBIs run correctly, but this one is being stubborn.

Not familiar with that TBI but it should have TPS and that possible cause both idle and WOT issue. Worth getting the voltmeter out and checking it.


Sent from my iPhone using Tapatalk

Quote:

---

Originally Posted by INSANEREINDEER

I've been helping my brother with his boat he bought last year (750 hrs). We've replaced everything the previous owner failed to do, got it cleaned up, and have almost everything working. The boat has a 350 Indmar Assualt TBI.

We are still having two major issues that I can not figure out.

First is a high idle. It cranks up an runs at 800, then after putting it in gear and driving for a bit, it stays at 1000-1100. I have yet to verify the throttle cable isn't sticking by pulling it off, but it is always resting on the stop so I don't think this is the issue. The engine needed a new IACV when he purchased it, so we replaced the IACV and TPS with one from an LT1 corvette from a parts store rather than Indmar. I also suspect this could be the issue, but doubtful with my experience in GM parts. I am going to get the parts we pulled from it, and verify the IACV is the same length. Yesterday, we also tried to swap it out with a MAP sensor I had laying around with matching P/N. No change. The only gasket/hose we have not replaced is the intake manifold to the head. Spraying carb cleaner around it doesn't change the RPMs. TBI gasket, TBI adapter plate gasket, PCV hose, CTS,& MAP hose all replaced. Flame arrestor was cleaned as well. We have hooked a laptop scanner to it my buddy had and all parameters seemed to be within reason. Where should I look next? I'm running out of ideas and I'm am very familiar with GM engines and EFI tuning.

The other issue is if you're idling and slam WOT, it bogs down and will die. I need to check the base timing. I also need to verify fuel pressure which I read was supposed to be over 40psi. Is there a screen in the tank on these boats that could possibly be clogged? It runs fine other than slamming WOT. Also starts with no issues.

Other than that, my last place to check is a compression test but that wouldn't cause the problems from my experience. I know it doesn't take much to make the TBIs run correctly, but this one is being stubborn.

---

Last summer we got to the lake, the boat fired right up and I noticed after I got it off the trailer it stayed at high idle. I couldn't understand why because it ran great the weekend before. I started looking around at the throttle body and noticed the TPS unplugged. I forgot to plug it back in after I was done working on it the week before. Plugged it back in and it ran perfect. I have done a lot on reading on my setup as this is my first TBI setup. The computer sets a fixed RPM when it doesn't get the correct signal from the TPS. Hope this helps and it fixes your problem. I did buy a handheld scanner to check all the sensors and parameters while its running. Most people don't do that, but I'm pretty anal.

I will double check the TPS sensor is acting within spec this weekend. It was replaced and I know it's not unplugged, but the new one could be trash from the parts store.

Quote:

---

Originally Posted by INSANEREINDEER

I will double check the TPS sensor is acting within spec this weekend. It was replaced and I know it's not unplugged, but the new one could be trash from the parts store.

---

If you can monitor voltage on your computer for the sensor, it should be very low at idle (.2-.4 I believe) to 4.5-5.5 volts at WOT. You can check this without the engine running with the throttle lever. The AC Delco number on my TPS is 19322821. I have the 2004 Assault with the MEFI-4a computer.

Quote:

---

Originally Posted by INSANEREINDEER

I will double check the TPS sensor is acting within spec this weekend. It was replaced and I know it's not unplugged, but the new one could be trash from the parts store.

---

There are several good resources for parts. Inboard Online is the authorized Indmar distributor (https://inboardonline.com/) Discount Inboard Marine is another.
(https://skidim.com) You can also contact Larry Engelbert at Indmar. He knows everything about these engines.

Quote:

---

Originally Posted by secondsupra2004

If you can monitor voltage on your computer for the sensor, it should be very low at idle (.2-.4 I believe) to 4.5-5.5 volts at WOT. You can check this without the engine running with the throttle lever. The AC Delco number on my TPS is 19322821. I have the 2004 Assault with the MEFI-4a computer.

---

Thanks. I have two GM GENIII engines I've tuned using HP Tuners so I'm familiar with what sensors are supposed to be reading. I believe this engine has MEFI 3.

I don't remember the P/N for the TPS we got, but it's the exact same style and fits. If it should be between .2/.4 makes me wonder if the internals are slightly different.

Do you have a P/N for the correct IACV and MAP? I want to double check these as well since we just matched them to what was previously on the boat which may not even be correct from the other hackjob repairs we found on this thing.

Quote:

---

Originally Posted by INSANEREINDEER

Thanks. I have two GM GENIII engines I've tuned using HP Tuners so I'm familiar with what sensors are supposed to be reading. I believe this engine has MEFI 3.

I don't remember the P/N for the TPS we got, but it's the exact same style and fits. If it should be between .2/.4 makes me wonder if the internals are slightly different.

Do you have a P/N for the correct IACV and MAP? I want to double check these as well since we just matched them to what was previously on the boat which may not even be correct from the other hackjob repairs we found on this thing.

---

MAP sensor number is 09359409. Don't have the IAC number handy, sorry.

Quote:

---

Originally Posted by secondsupra2004

MAP sensor number is 09359409. Don't have the IAC number handy, sorry.

---

So we have the correct map. The IACV we used is GM P/N 19351706. The TPS we used is a Duralast TPS115 which I believe is incorrect from looking at pictures. Same style, but the resistant values must be slightly different so this much be our issue.