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HI, I just put the motor back in my 86 spg after pulling it to freshen it up. new seals gaskets timing chain and guides.now i'm having idle problems and no tach. i've replaced the temp sensor / aic valve and checked the grounds and fuses. it starts right up but stalls unless i give it some throtle but after it runs a little while it idles good untill it reaches the temp for fans to come on then it idles a little high..and no tach i've change the ignition amplifier did'nt change a thing.. can anyone help me figure this out ?. Thanks
 

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The only time I had idle problems and a wildly inaccurate tach was when the electronic ignition module was failing. That was on a 1975 Triumph Spitfire with a failing Allison CDI ignition. The solution was to replace the ignition module with a Pertronix Ignitor.

The only times (note the plural) I had idle problems and no tach was with a failed alternator on a 1989 Range Rover on several occasions. It was a poorly designed Lucas alternator with a lifetime warranty. Eventually I got tired of taking the alternator back to the auto parts store, so I replaced it with a Bosch alternator out of a VW Passat. That solved the problem permanently.

Now, why would a failing alternator affect ignition? The tach signal was based on the field signal from the alternator, and when the diode pack failed, that AC signal failed too. It resulted in no charging, but because the alternator itself had failed the Charge light did not light up. The battery voltage dropped to around 9v, and both the ignition and the electronic fuel injection started operating intermittently, resulting in a very poor running, especially at idle.

Another time the battery grew very tired in my old Edwardian Gray '89 900S. After cranking to start the engine the car would run very poorly for a few minutes until the system voltage went above 9.2v, but the alternator on that car was strong and would recharge the tired battery enough that the car would run well again after a few minutes. That time getting a new battery permanently solved the problem.

If I were you, I would take the car into a battery shop for a free charging system check (unless you have your own load tester). Rule out a bad alternator and battery first, then start chasing ignition module problems. I infer from your login name that you have an SPG. I've never had to troubleshoot a faulty APC module, but I got offers to sell mine to mechanics when I was resuscitating my current '87 turbo. I drew the conclusion that they fail from time to time and are expensive to replace. Good luck.

Scott
 
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