50-60 MPH Shuddering - 1989 FJ62 175k miles

[haydonbetz]

Hey All -

Another highway shuttering/misfire thread.....

I have read all of the past posts and have tried most of the solutions but wanted to post my particular situation to see another set of eyes could give some insight.

Issue

• Between 50-60 mph at around 1800 rpm the car begins shaking seemingly from a misfire. If I lean into the throttle it worsens. If I let off the throttle and floor it it pushes through the 60mph range and lets me cruise after that. Also if I am in the gas and above 2000 rpm it will often, but not always, cruise through the 50-60 mph range. It happens more often going up slight highway inclines
• No CEL and no codes presented when I run diagnostic

Work Done

• Ignition system is 15k miles old
• New fuel filter
• New smog pump hose 1 (previous cracked)
• New air injection check valve
• EGR BB block off for diag

Where I am stuck

• Dont want to chase fueling issues because at higher rpm and higher speed the car will work fine
• Dont think its an electrical/vacuum issue because the specific mph range of the problem (I have visually checked wiring and vacuum hoses and don't see anything out of place)

Any thoughts of what direction to head next would be great.

 

[Kleatus]

Same in 3rd and OD?

Does EGR valve seat all the way?

Are coolant temp sender signals appropriate at ECM? (Wiring gets bad..3FE is sensitive to correct ECT..)

How about engine harness? I had an issue that presented as a "misfire" or rather massive series of misfires that was from injector wire degradation and shorting in the harness under the plenum, lots of heat there from EGR pipe...

 

[tmxmotorsports]

Check the air filter intake tube they dryrot and crack.

 

[sark]

consider your driveline as well, steering points being loose or u-joints on driveshafts?

 

[mabbet]

I had a similar issue and spent a lot of $ and time chasing ghosts. After reading the FSM and following the troubleshooting steps my problem turned out to be a bad ignition coil. Lesson learned... the hard way. Always consult the FSM first and follow the troubleshooting steps. The multimeter is your friend. Good luck.