98 SOHC running badly when cold

[kroed11581]

1998 Exploder, SOHC. In the cold, it fires right up, revs up to 1500, then down to about 600, if it doesn't die at this point, it'll kick up to 1500 again and back down to 600. Usually it dies somewhere in this roller coaster of RPM's. Once warmed up, it runs just fine - acceleration is great, power is great. Only happens when cold. Check engine light revealed only general misfire, and misfire on the driver's side banks. I replaced plugs and wires. Plugs and oil changes show no water in combustion chamber or oil, so I'm not thinking intake manifold gasket. O2 sensors are all new. Air filter is new. Cleaned IAC and MAF. Ideas? I thought maybe fuel pump or filter, but why misfire codes on one bank of cylinders? Engine seems to have plenty of power once warmed up.

 

[Ryan.]

I have been having a similar problem with my B4000. It starts up great, revs to about 2k and then slowly goes down until it dies. Gives codes for misfire on cylinders 4,5,6. If i give it gas for a couple minutes it will stay running. Performs normal after its warmed up.

So far I have replaced the coil pack, spark plug and wires, and fuel filter (all were in need of a change). Tested fuel pressure (68 psi) and tested vacuum (20 psi)

Anyone have any ideas???

 

[Nhaz]

Possibly temperature sensor. Not the one for the dash. the one for the computer.

My guess and its only a guess. that the computer is getting the wrong temp.

 

[kroed11581]

Solved

Turned out to be a leaking upper and lower intake manifold gasket. Replaced both, works like a charm. $18 parts, 3 hours time. Thanks for the help.