87 mustang low rpm shudder

87 mustang, 5.0 v8, have a shudder at narrow rpm range 750-1000, especially bad on hills and I live in San Francisco. Replaced distributor and set timing again and the shuddering range
narrowed...was up to about 1200. If I accelerate, out of the range, its fine. I use 91 octane...although maybe should have timed with 89. I'm stumped. Any ideas?
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well just a shot in the dark. I had a low rpm studder on a 97 escort and a simple adjustment on the throttle body to increase idle a tad worked like a dream... just an idea I'm far from an expert
snipped-for-privacy@att.net wrote:

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and

Yeaah, it's fine for you, but you only covered up an ISC problem..
You also could have converted it to a carbureter and done the same
Rest of you...DO NOT do that

I suggest you MAY have bad plug wires. I recently had the same symptoms... first time I had ever seen exactly that in 40 years on my cars, first time wires had failed in such a precise manner.
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Fastjack911 wrote:

Yeah, I had the same problem on a '98 Escort and I was sorely tempted to do the same thing, but it turned out that cleaning the MAF, fixing some issues with the EGR valve tubing and reseating all the vacuum connections I could reach fixed it.
I waste a lot of my life sitting in traffic (f#$ing New York City), increasing idle rpm means dollars wasted on gas for me.
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snipped-for-privacy@att.net wrote:

Your problem sounds like a ignition miss -plugs/wires. If its been a while I would do both just because....oh and replace that fuel filter, they are cheap and often overlooked at tune-up time. If it happens at high speed on not so steep hills it could be the torque converter. A good way to test it is to step on the brake slightly while its doing it. This disengages the TC lock up so you can tell if thats the problem. The type of gas won't matter if the timing is set correctly (spout disconnected(iirc) and at the correct RPM.
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Also clean your IAC valve.

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