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Intermitent idle/vaccum issues

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Hello, I have a new to me 02 rx300 with 170k on the clock. Im trying to figure out some issues Ive discovered and haven't found anything conclusive enough to fix. Thus, Im reaching out for help, all input would be appreciated.

The issue is partially intermittent. On idle when car is in gear and rpm is low ~600 there is a dead miss on 1-2 cylinders. It clears up as the rpm is increased. Additionally, the car suffers a low vacuum condition on occasion (largely after rough idling for awhile, or driving with the engine at low rpm). This loss of vacuum impacts the brake booster, which I find unacceptable and have been driving my other car (a 90' v12 jaguar xjs) instead. Not terribly practical.

I have generally looked for vacuum leaks without success. Have tried using smoke and noticed a flow of smoke to the booster area but haven't seen anything conclusive. Im also not convinced its a vacuum leak. It seems to happen intermittently, and like a switch if its good the car operates properly and other times, its rough and I ended up easing the car home without sufficient boosted brakes. Additionally, just by feel sometimes it seems the valve timing is not quite where it should be. Which has me suspecting the vvt system, which could potentially impact intake vacuum. I dont have all the codes with me but they were just general misses not cylinder specific.

I know almost nothing about the maintenance of the car, someones been here before. It has new plugs (didnt actually check back cylinders) and doesn't seem like an ignition issue. One of the screws on a vvt solenoid was replaced but the solenoid is original. I know bench testing solenoids isnt always an accurate way of determining if they are ok.

Im tired of having this issue and im ready to dig in to fix it. Let me know what things I should look at or address, Id love to hear your input. Im leaning towards replacing vvt solenoids, filters, and cleaning the iac valve (should I consider replacing the actual actuator?)


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