1986 420 SEL Hesitation
 

Hi, My 420 is experiencing engine hesitation problems when engine is warm. When you try to climb up hills it crawls. Also whne you floor it while driving on the highway it slowly gets up to speed but will stay there. No knocking, missing, or smoking. Changed the fuel filter but did not recitfy the problem. Any ideas? Thanks.

How many miles on your 420? What recent basic maintenance was done such as plugs, cap/rotor?

Just got
 

Hi, I just got it few weeks ago and just started to drive. It was purchased from Canada and has 290,000 Kil. on it. It was always dealer maintained since new and I purchased from original owner. He had just had the rotor replaced and all. The plugs ect also look new. Problem has just started recently.

Start at basics
 

You need to satisfy, your need to know what makes it tick,you know the plugs are good ,the rotor is good,the cap is good the next item is the wires(plug)?Check them with ohm meter and wind one that has to much resistance.If this is OK then move on to what can make it not pull?try to look into the on off ratio get the fuel balance set and the o2 sensor it may be telling the eha that the condition is far to rich if so you will not get the fuel needed to make it perform.one of the least wished for is the old catalytic converter being plugged.But look first to these other things it will keep you occupied for a while.JNT:idea2:

Check the air flow sensor pot. They go bad and cause this symptom. They sense changes in throttle and tell the computer to enrichen the mixture when accelerating. When broken the car hesitates. It also sounds like your mixture is not properly adjusted. ALso check that your oxygen sensor is working.