Hi Guys,
I recently completed a new engine, for my $600 Vert and it's on the road. It has been running for two weeks now but the idle was so bad, I didn't drive it anywhere. I am running a 331 with GT40Y heads, Cobra intake, 1.72:1 rockers C&L 77MM cold air with 24# calibration and TFS stage 1 cam. This is in a '94.
I started by putting 1.5 turns on the air bleed. Then I opened the TB until the engine would idle with the spout out. This took a few tries until I had an idle of 900 RPM with spout out and ISC disconnected. The engine was still surging and because the ISC and spout were out, the only thing that could cause a surge was MAF problems. Looking at the MAF intake, I clocked it from 12 to about 5:00. On restart, I found I had a stable 900 RPM idle. Then I closed down, on the TB, until I had about 600 RPM. Every time the fan would ome on, the engine would die because the ISC was disconnected. I shut down, disconnected the battry and jacked up the car so I could start work on the header to "H" pipe leak I had.
It took about 10 minutes to see where the leak was and fix it. Tip: If the "H" pipe side of the flange is not pulled up evenly, around the pipe flare, you can get leaks like I did. To fix it, I backed off on the bolts till they were loose. I used a 3/8" punch to tap on the flange and get it square with respect to the end of the "H" pipe flare. Then I tightened the bolts back up.
After reconnecting the battry, the car started right up, (no exhaust leak- YEAAA), and settled into a 800 RPM idle. As soon as it went into closed loop, the idle dropped down to about 600 RPM on my tach. I know thats lower than the published idle RPM but maybe my tach is off? Anyway, the engine cycled through three electric fan cycles. The first one almost killed the engine but the next two were fine. After the EEc learned the new idle, all was good. I have a nice, slow, lopey idle.
One popular work around is to use the air bleed or TB to get a 900 RPM idle. If you do this, you get a stable idle, but then you have to deal with a hanging idle problem. The ISC is used like a dash pot on a carb. The ISC circuit does not use feedback so it prepostions on deceleration. If you have to much TB or air bleed, this prepostion will result in a 1200-1500 idle RPM on decel. Thats what mine was doing.
Hope this helps,
Eric
I recently completed a new engine, for my $600 Vert and it's on the road. It has been running for two weeks now but the idle was so bad, I didn't drive it anywhere. I am running a 331 with GT40Y heads, Cobra intake, 1.72:1 rockers C&L 77MM cold air with 24# calibration and TFS stage 1 cam. This is in a '94.
I started by putting 1.5 turns on the air bleed. Then I opened the TB until the engine would idle with the spout out. This took a few tries until I had an idle of 900 RPM with spout out and ISC disconnected. The engine was still surging and because the ISC and spout were out, the only thing that could cause a surge was MAF problems. Looking at the MAF intake, I clocked it from 12 to about 5:00. On restart, I found I had a stable 900 RPM idle. Then I closed down, on the TB, until I had about 600 RPM. Every time the fan would ome on, the engine would die because the ISC was disconnected. I shut down, disconnected the battry and jacked up the car so I could start work on the header to "H" pipe leak I had.
It took about 10 minutes to see where the leak was and fix it. Tip: If the "H" pipe side of the flange is not pulled up evenly, around the pipe flare, you can get leaks like I did. To fix it, I backed off on the bolts till they were loose. I used a 3/8" punch to tap on the flange and get it square with respect to the end of the "H" pipe flare. Then I tightened the bolts back up.
After reconnecting the battry, the car started right up, (no exhaust leak- YEAAA), and settled into a 800 RPM idle. As soon as it went into closed loop, the idle dropped down to about 600 RPM on my tach. I know thats lower than the published idle RPM but maybe my tach is off? Anyway, the engine cycled through three electric fan cycles. The first one almost killed the engine but the next two were fine. After the EEc learned the new idle, all was good. I have a nice, slow, lopey idle.
One popular work around is to use the air bleed or TB to get a 900 RPM idle. If you do this, you get a stable idle, but then you have to deal with a hanging idle problem. The ISC is used like a dash pot on a carb. The ISC circuit does not use feedback so it prepostions on deceleration. If you have to much TB or air bleed, this prepostion will result in a 1200-1500 idle RPM on decel. Thats what mine was doing.
Hope this helps,
Eric