1997 LX450 - Shudder under load at 50-60mph

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Oct 28, 2019
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Location
Berkeley, CA
Experiencing a shudder under load a 50-60 mph. It's like a momentary loss of power that pulses until I reduce speed or give it gas. Not sure if this is a tranny issue, driveline issue, or something else. It feels like it is in the front end almost like a tire is skipping or something like that.

Recently replaced the rear driveshaft for a bad slip yolk. The front drive shaft has new OEM u-joints about 20k miles ago and was recently lubed. I just did a rebuild on the front left steering knuckle as the seal had gone bad and grease and gear oil had mixed in knuckle and in the diff housing. RCV birfields and shafts. This is a supercharged engine. No noticeable tranny issues (except for typical reverse problem) with recent fluid change about 15-20k miles ago and new filter. 35" tires on OME kit with OME caster correction. Recent replacement of fuel pump with OEM denso pump.

Any ideas on what might be causing this problem? I am at a loss.
 
I have a similar setup and similar shudder. '97 LX450, supercharged, 35" tires. I have called it a "stumble" around 2000 RPMs when going up a hill. To me it feels like a fuel delivery issue, but I don't know that for a fact. Overdrive off or give it more throttle and it works through it. Is this why people upgrade injectors (Supra) or add a 7th injector?

Similar symptoms on a '94, and other links in this thread. I don't see it resolved. Methanol injection is mentioned by many SC drivers, but I do not have it.
https://forum.ih8mud.com/threads/en...so added headers and a 3" exhaust (as did I!)
 
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OP says it fixed itself, maybe bad gas. Another said vacuum leak, tightened valve cover bolts at the rear.

Torque converter lock up solenoid speculation, no conclusion that I can see.
 
The problem traced back to an intermittent ground issue with the main engine harness, I built a temporary bypass harness for the fuel injectors until I can get a new main engine harness.
4 pages, good troubleshooting. I have repairs in the harness by the EGR pipe and this my be my issue, not sure. SC may run hotter exhaust, and the change in location of the MAF stretched the harness towards the passenger side.

 
Spark plug wires:

Wire harness near the EGR, links to 6 other threads
 
OP says it fixed itself, maybe bad gas. Another said vacuum leak, tightened valve cover bolts at the rear.

Torque converter lock up solenoid speculation, no conclusion that I can see.
Thanks doc-random. Turns out it was a vacuum leak from the valve cover, same as the previous post you highlighted. Two loose bolts on the valve cover (the far back ones on the passenger side). They were barely finger tight. A quick tightening and the hesitation and stuttering is gone! What a weird thing that the same thing happens at the same place, maybe the additional heat from the EGR port over there along with the expansion and contraction causes those two bolts to loosen up over time.

Thanks again!
 
IH8MUD for the win! You are welcome, I'm glad it worked for you.
 

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