High idle and trans shifting issues
05-09-2010, 08:49 PM
#1
High idle and trans shifting issues Ok I just bought a 94 z28 with a hotcam and full boltons. Also has a cheap 2000-2500 stall and 373s. With all these mods the prior owner never got it tuned.
The opti went out about a month ago and he replaced the whole ignition system. After he did it has been idling really high. Then after it started idling weird the trans started shifting late, at like 3200 rpms and shifts pretty freakin hard.
I've checked for disconnected vacuum lines and they all seem to be fine. The car idles at about 1500 rpms cold and around 1000 warm. If I drive it a while and stop it will idle at around 900 and sometimes drop to around 700-800 where you can hear the cam hit a lick and it will choke out and die.
I'm no sure if the idle problem and tranny are related but have a feeling they are since both problems came up at the same time. I bought the car "with a bad transmission" but it doesn't slip and holds all gears fine. I'm thinking maybe the iac could be bad or tps but I'm not getting a check engine light and haven't had it scanned. When I go wot it will not rev over 3000 before shifting into the next gear and I don't think the converter is locking neither.
I know Lots of this is due to the car not having a tune and I'm planning on a dynotune before long but the prior owner drove the car for almost a year with no weiird problems like this. Any suggstions appreciated.
Oh yeah. Car has a big holley throttle body but I'm not sure what size.
The opti went out about a month ago and he replaced the whole ignition system. After he did it has been idling really high. Then after it started idling weird the trans started shifting late, at like 3200 rpms and shifts pretty freakin hard.
I've checked for disconnected vacuum lines and they all seem to be fine. The car idles at about 1500 rpms cold and around 1000 warm. If I drive it a while and stop it will idle at around 900 and sometimes drop to around 700-800 where you can hear the cam hit a lick and it will choke out and die.
I'm no sure if the idle problem and tranny are related but have a feeling they are since both problems came up at the same time. I bought the car "with a bad transmission" but it doesn't slip and holds all gears fine. I'm thinking maybe the iac could be bad or tps but I'm not getting a check engine light and haven't had it scanned. When I go wot it will not rev over 3000 before shifting into the next gear and I don't think the converter is locking neither.
I know Lots of this is due to the car not having a tune and I'm planning on a dynotune before long but the prior owner drove the car for almost a year with no weiird problems like this. Any suggstions appreciated.
Oh yeah. Car has a big holley throttle body but I'm not sure what size.
05-10-2010, 05:38 PM
#4
You need to have it scanned for codes anyway. There are some codes that do not set the SES light.
You should also get a tune. As mentioned, it can clear up a ton.
If your TPS values are off, then the car won't shift at WOT. Some aftermarket throttle bodies (like the Holley) when at WOT put the TPS past it's max range and the transmission won't shift.
Get a multimeter and check the TPS. With the key on, engine off, the blue signal wire of the TPS should read between .2 and .9v (somewhere in the middle is preferred). Then, have someone step on the gas WOT (don't use your hand to open the throttle body) and monitor the voltage then. Should be about 4v higher than your original reading. If it isn't, you will need to slot the mounting holes of the TPS to bring the range into spec.
I should also note that if it's a 58mm throttle body, it's not hurting you in any way. You can fix your issues with the throttle body you have.
You should also get a tune. As mentioned, it can clear up a ton.
If your TPS values are off, then the car won't shift at WOT. Some aftermarket throttle bodies (like the Holley) when at WOT put the TPS past it's max range and the transmission won't shift.
Get a multimeter and check the TPS. With the key on, engine off, the blue signal wire of the TPS should read between .2 and .9v (somewhere in the middle is preferred). Then, have someone step on the gas WOT (don't use your hand to open the throttle body) and monitor the voltage then. Should be about 4v higher than your original reading. If it isn't, you will need to slot the mounting holes of the TPS to bring the range into spec.
I should also note that if it's a 58mm throttle body, it's not hurting you in any way. You can fix your issues with the throttle body you have.
05-10-2010, 11:07 PM
#5
Ok, I replaced the TPS and the car idles like it should. No more 1500 rpm idling and it seems smoother when accelerating. I bought a multimeter to so now I can start finding out what the cars doing without throwing parts at it.
I drove the car some more this evening and the transmission is still acting up. Its only wanting to shift at around 3000 rpms no matter how much throttle I give it. At low throttle it will rev up to 3000 and then shift hard. At WOT it will still cycle through the gears at 3000 rpms. I have no passing gear and the torque converter isnt locking. The tranny however is not slipping. I can pull it down a gear and gun it and it downshifts fine and doesnt slip or do anything weird.
I really think this issue is something electrical or something in the valve body. It just shifts too good and drives to good to need a new transmission, and it sure would be nice if I dont have to replace it and use the money for paint.
Im gonna get the car scanned as soon as I find someone with an obd1 scanner. Oreillys didnt have one and they said nothing would come up if the lights not on
I drove the car some more this evening and the transmission is still acting up. Its only wanting to shift at around 3000 rpms no matter how much throttle I give it. At low throttle it will rev up to 3000 and then shift hard. At WOT it will still cycle through the gears at 3000 rpms. I have no passing gear and the torque converter isnt locking. The tranny however is not slipping. I can pull it down a gear and gun it and it downshifts fine and doesnt slip or do anything weird.
I really think this issue is something electrical or something in the valve body. It just shifts too good and drives to good to need a new transmission, and it sure would be nice if I dont have to replace it and use the money for paint.
Im gonna get the car scanned as soon as I find someone with an obd1 scanner. Oreillys didnt have one and they said nothing would come up if the lights not on
05-11-2010, 04:05 PM
#6
I figured it out. The prior owner bent the throttle stop so that it was not against the screw in an attempt to make the car idle lower. The car was idling high because of a bad tps which I replaced and I also bent the throttle stop to it's original position.
The car is idling perfect now and shifting like it should. I'm just posting this info to help someone if they are having a similar issue and are searching for an answer.
The car is idling perfect now and shifting like it should. I'm just posting this info to help someone if they are having a similar issue and are searching for an answer.
