88 Ranger 2.9L idle surges on start up when cold

[88 XLT Ranger]

Need help

My 88 Ranger 2.9L V6 idle surges on start up when cold after it warmes up it idles at 900rpm's. Why would it do this surge in RPM's when cold?

 

[RonD]

I think that year had a MAP sensor, located on the firewall, it has a vacuum line connected to it, make sure that vacuum line is air tight, not cracked.

The IAC(idle air control) on the upper intake can get dirty and sticky, this is an air valve controlled by the computer to set a steady idle.
The IAC can be removed and cleaned.
It is normal for computer to set a high idle when engine is cold, so IAC valve is opened more, if it is sticky at that point then idle can surge as computer tries to stabilize it, once engine is warm the valve can close more where it might slide without sticking so a stable idle.
Idle should be about 700rpm warm, check for vacuum leaks, that raises the idle.
hard vacuum lines should be replaced, if they are not cracked now they will be sooner than later.

 

[jhammel85]

I just responded to your trans problem. Check the IAC out but there's a possibility that the trans modulator is dead allowing a vac leak or the hose itself is leaking. Check out the hose that comes off the tee near the fuel pressure regulator that goes behind the engine to the trans.

 

[88 XLT Ranger]

I just responded to your trans problem. Check the IAC out but there's a possibility that the trans modulator is dead allowing a vac leak or the hose itself is leaking. Check out the hose that comes off the tee near the fuel pressure regulator that goes behind the engine to the trans.

Thank you both so much its very much appreciated I will check everything today