Wierd throttle issue after redoing intake manifold spacer - Cobalt SS Network



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Old 05-13-2017, 02:23 PM   #1
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Wierd throttle issue after redoing intake manifold spacer

I just finished up installing a second h/e as well as replacing my phenolic spacer so as to setup the PCV like it was before. My IAT2 temps are great and my car seems to be running good but it has high idle (2,000 RPM) and will actually rev if I am going down the highway and then put it into neutral. Watching the OBD scanner I could see that my absolute throttle position never dropped below 23% and when it would rev it would go as high as 37% on it's own. Problem is I don't know how close to normal this is. I have checked extensively for vacuum leaks using the carb cleaner method. I could not find anything that even hinted at a vacuum leak. I'm thinking it would take a decent sized vacuum leak to be causing that on it's own. My car will cruise at 40 mph in 5th gear at idle. I'm trying to see if the people that tuned me have any idea (Trifecta as I am 2006 LS) but responses from them aren't always timely so we'll see.

For the phenolic spacer installation I applied 2 coats of copper spray a gasket to each side of the provided paper gaskets. I then installed them shortly after but allowed it to tack up a bit.

I can confirm I don't have any vacuum leaks along the top side but I haven't been able to spray the bottom side with carb cleaner to test. I sprayed all around the supercharger gasket and no leaks detected. I sprayed at every vacuum side connection and around injectors and again, no leaks detected. I will test the bottom side of the intake manifold here shortly but if it shows no sign of vacuum leak I don't know what to do next. I once tried to use an LNF intake gasket because that is what ZZP accidentally sent in the SC kit. I had a vacuum leak and it acted nothing like this. I was also easily able to detect it with the carb spray test. I also detected a vacuum leak around some injectors before with this method and again it wasn't acting anything like this. The idle doesn't fluctuate it is just way high.

Edit:Trifecta got back to me and said could be the Throttle body. I did something dumb when I was resembling. I have random spare parts accumulated and I see what looks like it would work for a fuel rail extension cord because it's a real pita to connect normally. It connected right up and I threw a bunch of codes when I first went to start up. There were codes about my fuel and map sensor as they are on that same harness, but somehow I also tripped a couple codes for the throttle body which I thought was weird because they were connected right. Turns out my "extension" is actually a throttle body adapter and it doesn't go to the same pin on the other side. So I am wondering if somehow the TB and fuel injectors/map share some circuit through the ECU and I screwed up my TB or TPS by crossing the wires with that incorrect adapter.

Last edited by jdbaugh1; 05-13-2017 at 06:58 PM.
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Old 05-13-2017, 02:31 PM   #2
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Vac leaks that big would be setting codes.
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Old 05-13-2017, 04:26 PM   #3
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Another thing I forgot to mention was when I was trying to see what it would do under boost I got clear up to 10 psi and held it but my wideband didn't move from stoich unlike usual where the fuel mixture is enriched under acceleration. I wasn't going to push it past 10 PSI running ~14.5 AFR. My methonal injection was working properly and that combined with my low IAT2 temps must have been enough to keep the engine from knocking even though it was lean. I do have my lower power tune flashed with timing advance around 20 degrees with WOT.
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Old 05-16-2017, 06:51 PM   #4
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Well I just installed a new LSJ throttle body and my car is running the exact same as it was before and I have no idea what the cause could be or what to do next.

Edit: Guess I am going to try swapping out the ECM.

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Old 05-17-2017, 11:52 AM   #5
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Can you log fuel trims? Sounds like maybe your intake is leaking or the maf isnt seated/tight
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Old 05-17-2017, 01:51 PM   #6
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Quote:
Originally Posted by Slowbalt2000 View Post
Can you log fuel trims? Sounds like maybe your intake is leaking or the maf isnt seated/tight
I can monitor fuel trims with my OBD bluetooth adapter but can only log through Trifecta. Total is around 10% at my over 2,000 rpm idle but that could be because of my tune as well. If it was a vacuum leak big enough to cause this I would expect my fuel trims to be pegged and to throw a lean code. I'm honestly starting to think I corrupted or screwed up my ECM in some way when I used the incorrect adapter for my fuel rail. Supporting this theory is when I first turned the ignition on, with the wrong adapter connecting the fuel rail, it was also throwing codes for the throttle body which didn't make any sense to me at the time. I'm thinking I accidentally routed too much voltage into the TB circuit in the ECM or something of the sort because there is no other reason for the fuel rail circuit to throw off the TB circuit. When I corrected the fuel rail harness the TB code went away with the other codes. I also used nearly 3 cans of carb cleaner spraying around any potential spots for vacuum leaks multiple times. According to fuel trims at cruise my MAF is working properly.

Also, according to Trifecta my acceleration enrichment is driven, at least partially, by throttle position. It then seems likely that is also the cause of my AFR staying at stoich up to 10 psi but I didn't push it any harder with it staying lean.

I have a replacement ECM coming in the mail this week. I will do the security relearn and give er a rip and report back here and let you know if that was the problem or not although I don't think anyone would ever do what I did so this will probably never be an issue for anyone else.
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Old 05-19-2017, 01:09 PM   #7
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Well I replaced the ECM, went through security relearn, and then flashed my tune and it's doing pretty much the same thing. Weird revs when I push in the clutch and no enrichment on acceleration are still there. Weird thing is that idle is slightly lower at around 1,650 RPM. So then I replaced my supercharger to IM gasket, just in case it somehow had a leak, and that doesn't appear to have changed it at all.
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Old 05-19-2017, 03:57 PM   #8
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Alright so now I am fairly confident that my MAP sensor is causing all of this trouble. I unplugged the MAP and fired up my car and idle RPM went up and down. I shut off the car and plugged back in the MAP and everything was back to normal. My idle was around 900 RPM and my fuel trims were back in the high negatives like they were before. I went out for a drive to see if it would enrich under acceleration and it still wouldn't. But then I shut off my car and turned it back on and the idle was back up around 2,000. I think I fried something in the MAP sensor when I incorrectly connected the fuel rail since the MAP is also connected through that same harness. So probably going to prevent me going to autocross this weekend but I am just happy that I think I found the problem.
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Old 05-19-2017, 04:20 PM   #9
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have a look at your map sensor readings with your scanner, see how they look. sounds like you have found the issue though, just good to confirm the reading before you buy parts.
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Old 05-19-2017, 06:39 PM   #10
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It was the MAP sensor. I'm back to my normal bouncy idle and fuel trims. The acceleration enrichment is kicking in correctly. It's running good now.

And Sharkey I did look at the MAP reading on the scanner and it was not reading correctly. I don't know why I didn't check the MAP sensor earlier. I just assumed if a sensor was throwing something that far out of whack it would throw a code. My car was doing some pretty wild ****. Revving to 5500 rpm sometimes when I pushed the clutch in.

This is why you don't just throw parts at something lol. Oh well spare parts for the future.
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