BEGi S4 idles at 4500 rpm
03-20-2008, 09:54 AM
#1
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BEGi S4 idles at 4500 rpm
I just finished the installation of a BEGi S4 kit on my '99, and when I attempt to start the car, it quickly climbs up to 5000 rpm, dropping to 4500 where it stays until I shut it off.
The details:
'99 w/ stock engine
BEGi S4 w/ 2560, Xede, 550s, Tial ewg
Enthuza 3" exhaust
Before installing the turbo kit, I was running an MP62, so I had to relocate the TPS and throttle body back to the stock location. When running the blower, I had to disconnect the coolant passage running through the throttle body housing. With the blower, I was running stock timing.
In troubleshooting the issue, I tried disconnecting the TPS, as well as everything else on the TB, to include the throttle cable. I've searched for a vacuum leak, although the smooth revving to 5k makes me think that there isn't a leak. Every time I've seen vacuum leaks in the past, the idle fluctuates roughly.
I have a notion that the MAF might simply be jacked up, but don't know how to find out. During the installation, there was a good bit of time where the MAF was exposed while awaiting a compressor inlet pipe, so I guess it could have been fouled by the elements.
If anyone has any suggestions, I would greatly appreciate it.
John
The details:
'99 w/ stock engine
BEGi S4 w/ 2560, Xede, 550s, Tial ewg
Enthuza 3" exhaust
Before installing the turbo kit, I was running an MP62, so I had to relocate the TPS and throttle body back to the stock location. When running the blower, I had to disconnect the coolant passage running through the throttle body housing. With the blower, I was running stock timing.
In troubleshooting the issue, I tried disconnecting the TPS, as well as everything else on the TB, to include the throttle cable. I've searched for a vacuum leak, although the smooth revving to 5k makes me think that there isn't a leak. Every time I've seen vacuum leaks in the past, the idle fluctuates roughly.
I have a notion that the MAF might simply be jacked up, but don't know how to find out. During the installation, there was a good bit of time where the MAF was exposed while awaiting a compressor inlet pipe, so I guess it could have been fouled by the elements.
If anyone has any suggestions, I would greatly appreciate it.
John
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03-20-2008, 10:06 AM
#6
It takes air to spike the idle like that. You need to find out where the air is coming in. A small vacuum leak might cause the idle to fluctuate, but a big one will make it act like the throttle is open. The turbo kit shouldn't have anything to do with this, but I'd recheck everything you had to do to remove that supercharger.
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03-20-2008, 10:11 AM
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One simple suggestion... make sure your throttle is not sticking. Right before I did my turbo install I thoroughly cleaned the engine bay at the car wash, maybe you did the same. Afterwards the throttle stuck a bit and the engine stuck at a 2500 rpm idle or something like that. I found the problem, lubed the throttle, problem gone.
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03-20-2008, 11:23 AM
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As far as the other posts about the TB sticking open and/or not sealing properly, I'm planning on checking it out thoroughly and getting back to y'all. With the throttle cable disconnected, I was assuming too much that it couldn't be the TB. I'll pull the throttle inlet tube again and find out what the blade on the TB looks like.
Thanks much to all who have replied.
John
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03-20-2008, 12:24 PM
#11
First rule - always go back to what you just did. You've had to re-seal the throttle body to the intake manifold. It's unlikely the inside of the throttle body suddenly changed or something happened to the butterfly. It's far more likely your gasket or RTV didn't get you a good seal around the body. Or you forgot to put some sort of cap back on a vacuum nipple. Heck, with a leak that size I'd be looking at the hose to the brake booster to make sure it was attached.
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03-20-2008, 01:32 PM
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Even with the cable disconnected the throttle could still stick. In fact mine was sticking at the throttle mechanism itself. Not on the inside in the throttle bore, but on the outside (spring, bushing, etc). I just sprayed it with a light coat of penetrant and it was fine.
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03-20-2008, 04:12 PM
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First rule - always go back to what you just did. You've had to re-seal the throttle body to the intake manifold. It's unlikely the inside of the throttle body suddenly changed or something happened to the butterfly. It's far more likely your gasket or RTV didn't get you a good seal around the body. Or you forgot to put some sort of cap back on a vacuum nipple. Heck, with a leak that size I'd be looking at the hose to the brake booster to make sure it was attached.
Even with the cable disconnected the throttle could still stick. In fact mine was sticking at the throttle mechanism itself. Not on the inside in the throttle bore, but on the outside (spring, bushing, etc). I just sprayed it with a light coat of penetrant and it was fine.
BTW: One of the original thoughts I had regarding this was that maybe the timing had been advanced a ton somehow. It seems to me that if that was so, that the idle would be much higher as well, so I pulled the Xede harness and routed the wiring through the stock ecu. Nothing changed.
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03-20-2008, 09:23 PM
#18
Throttle cable too tight, throttle body stuck open would be my first check. 4500rpm is a massive air leak. I recently removed an MP62 from my car, and I had to readjust the throttle cable quite a bit. Did you remove or move the TPS sensor around? That would require recalibration, unless you have an ECU that adjusts the TPS signal instead of having to do it at the throttle body with a voltmeter. On a 99, the coolant lines to the throttle body have no effect on the IAC and idle. The IAC valve is completely different than the 90-97 units.
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03-21-2008, 11:15 AM
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Yes. When at 4500-5000 it was reading 20 in vac.
Last night we sprayed some starting fluid around to see if the idle changed, and it fluctuated a ton when spraying over the fuel rail and TB. I was pretty certain that I had found the vacuum leak at the top of the TB, where the idle adjustment screw ends. I jammed a piece of gasket material down between the TB and IM and it didn't have any effect.
As mentioned, I had the throttle cable completely disconnected for a time, and the idle remained at 4500 rpm. Additionally, when I removed the MP62 and installed the turbo, I had to relocate the TPS back to the stock location along with the TB.
Last night we sprayed some starting fluid around to see if the idle changed, and it fluctuated a ton when spraying over the fuel rail and TB. I was pretty certain that I had found the vacuum leak at the top of the TB, where the idle adjustment screw ends. I jammed a piece of gasket material down between the TB and IM and it didn't have any effect.
As mentioned, I had the throttle cable completely disconnected for a time, and the idle remained at 4500 rpm. Additionally, when I removed the MP62 and installed the turbo, I had to relocate the TPS back to the stock location along with the TB.
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