Hey all, I recently replaced the fuel pump and throttle position sensor on my MPFI V6 3.1L RS. However now a new issue has popped up, when coming to a hard stop or sitting with my foot on the brake, the rpm's do not hold a correct idle of around 550. They seem to hunt around for the best idle, and occasionally plummet to the point of stalling. This will also happen if I am coasting under 15mph. Most times it catches itself and the rpm's will spike back up to 1,000-1,500. I have tried an idle relearn that is very hotly suggested on the board for this type of engine, but when doing this, I noticed my fan does not work either after replacing my fuel pump and TPS. I had thoughts of a bad Idle Air Control (IAC), brake booster going bad/hose leak, and possibly the fan switch/engine temp sensor in front of the block being bad and somehow messing with the ECM. Any thoughts or insight is greatly appreciated, as I'm planning to go on vacation soon driving this car

 

Brake booster

Those other 2 "explanations" are about as likely as blaming it on the space aliens

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I would also suggest considering checking/looking at the fuel pressure regulator - sometimes you can get raw fuel into the vacuum system when it goes bad- I had similar issues on my car.
Too cheap to pay a legit mechanic to find the issue, I replaced the ignition coil, distributor, injectors, IAC, and brake booster hose.
In the end it was a torn fuel pressure regulator membrane.
had to get the security torx driver and the flat rubber fuel pressure regulator membrane and she runs like a champ now.