1989 Silverado Idleing Problem

[Camaro_nut2001]

Hello, I have a 1989 Silverado 1/2 ton 4X4 with a 305, automatic. It has the throttle body. My problem is the truck idles way to high when warm, really all the time but is faster when warm. I have replaced the TCS, IAC & the TPS. Nothing has helped. I have cleaned the throttle body plates & shaft & checked for vacuum leaks everywhere I can think of including the intake. Also, the trans shifts too late & jerks from 1st to 2nd & it won't adjust with the cable. I have it almost all the way in where it should shift real fast & soft but it doesn't. Right now I have the TPS & the TCS unplugged & it idles great just a little hard to start. I haven't driven it to see if the lower idleing has affected the trans shifting as I want it right & all the sensors plugged up before I drive it again. It is not throwing any codes with everything plugged up. I traded for this truck about a month ago & it was idleing a little fast but nothing like it is now. I'm stumped on the trans shifting also. I have a '96 Suburban & it runs, shifts etc..... great with 279,000 on it. If ya'll could give me some suggestions it would be soo appreciated. Thank you.

[mountie]

Originally Posted by Camaro_nut2001

Hello, I have a 1989 Silverado 1/2 ton 4X4 with a 305, automatic. It has the throttle body. My problem is the truck idles way to high when warm, really all the time but is faster when warm. I have replaced the TCS, IAC & the TPS. Nothing has helped. I have cleaned the throttle body plates & shaft & checked for vacuum leaks everywhere I can think of including the intake. Right now I have the TPS & the TCS unplugged & it idles great just a little hard to start. I haven't driven it to see if the lower idleing has affected the trans shifting as I want it right & all the sensors plugged up before I drive it again. It is not throwing any codes with everything plugged up. I traded for this truck about a month ago & it was idleing a little fast but nothing like it is now. I'm stumped on the trans shifting also. I have a '96 Suburban & it runs, shifts etc..... great with 279,000 on it. If ya'll could give me some suggestions it would be soo appreciated. Thank you.

(You wrote) : ....."Also, I have it almost all the way in where it should shift real fast & soft but it doesn't...." >>>> What are you referring to???

I am racking my brain...... it seems to me, I had the similar idle problem years ago...... I am trying to remember what the fix was.....(TBI gasket?) (Timing?)


(You wrote): "...the trans shifts too late & jerks from 1st to 2nd & it won't adjust with the cable...."
The Transmission -Throttle Valve Cable MUST be adjusted correctly...... (a 1/8th inch is a big difference)..... have a tranny guy that knows how, to adjust it, do it.

[Camaro_nut2001]

Originally Posted by mountie

(You wrote) : ....."Also, I have it almost all the way in where it should shift real fast & soft but it doesn't...." >>>> What are you referring to???

I am racking my brain...... it seems to me, I had the similar idle problem years ago...... I am trying to remember what the fix was.....(TBI gasket?) (Timing?)


(You wrote): "...the trans shifts too late & jerks from 1st to 2nd & it won't adjust with the cable...."
The Transmission -Throttle Valve Cable MUST be adjusted correctly...... (a 1/8th inch is a big difference)..... have a tranny guy that knows how, to adjust it, do it.

I was referring to the shift detent cable being almost all the way it but I found my problem on both issues. The shift cable was sticking & the fast idle is a worn throttle shaft & I have a WTB ad on here now. Thanks for your interest in tryin to help me.