When I start my 98 explorer xlt 4.0 SOHC in the mornings the engine immediately races to 2500-3000 RPM and drops to less than 1,000 RPM, then back up, then down and sometimes dies, at low RPMs it runs real rough. All of this happens until the engine gets good and warm.
Any ideas what it could be or cost to repair?
Sounds like intake manifold gaskets. If you had warranty work done on your front timing chain tensioner, they should have been changed. Usually its the lower manifold gaskets that cause the problem, but in my case I had the timing tensioner replaced at the dealer, ended up replacing the intake manifold gaskets myself and upon reassembly discovered that the upper manifold wasn't properly torque at the dealer. Relatively easy replacement job with manual for reference. You could also check the Idle Air Control (IAC) valve, clean it out along with the air passageways, but in all likely, you have a gasket leak.
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