bes4000

After a 3-4 minute idle warm-up the rpms dropped and the idle became rough. Only rough below 2000 rpm. Driving below 2000 there is a hesitation, but above that it runs great. No smoke out the back and no backfire. Any thoughts?? Thanks.

BS
85 4kqs

PJM99

Mine did that for awhile. Low RPM is would hesitate would clear up on the highway. I check everything ended changing the plugs and wires, nothing. Changed out the fuel filter and haven't had a problem since.

mt6127

Have you looked at the intake boot and vacuum lines? Next I'd look at the FI ground wires and temp sensor. The NCT temp sensor is on the bottom side of the flange coming off the block by the 1-2 spark plugs. The top temp sensor on the flange is for the temp guage, the bottom feeds into the ECU. try cleaning up the contacts and measure its resistance. Should measure 2.5K ohms or more below room temp. Resistance should drop with warm engine (I can't find the exact number but I recall something like 600 ohms or less with a warm engine). Part should cost $25-$30. Last is to look at the O2 sensor (you'd need to measure the control current at 3000 RPM and look for fluctuates..)