A while ago I blew one of my stock turbo coolant hoses. Which was a lot of fun to replace, since I have fat stupid hands.

After the fact, my car has developed a distinct buzzing sound under the rear of the UIM, on the side near the turbos.
The buzzing happens intermittently through the rev range. Blipping the throttle and letting off will cause it, and it also seems to happen right around light load cruising at 2500-3000rpm.
And, when I take the ACV line off and listen it seems to coincide. Should the ACV line kindof roar at me coming off throttle?

I've acquired a couple spare ACV's to swap in. Also considered the ISC. Anyone experienced similar symptoms or have any clever ideas before the car goes under surgery?

 

The only time I ever heard buzzing from there was with an injector related incident IIRC. It was hard for me to believe until further testing confirmed it. Search on that for other threads.

 

I have had numerous cars come in with "buzzing" ISC valves, quick test- unplug it and see if the noise stops.

 

Hmm. I hope that's not the issue. Do you recall other related symptoms?

It has been idling a little weaker. Is the ISC on the turbo side of the engine?
I guess the sound could also be described an an aggressive hissing.

Thanks for the help

 

The ISC is located on the UIM on the firewall side next to the throttle body. If the buzzing is from the turbo area I doubt it's your ISC but its easy enough to check. There is a electrical bung in the back. The ISC solenoid is silver with a black base and has a white connector. Just unplug it. Bazai has a good picture of it on their site under the block off plate instructions. Just make sure the A/C is off.

There are a lot of random bolts and connectors around the stock turbos. Check that you didn't knock any loose during the coolant line repair or that one hasn't worn away. I had a similar problem and it turned out that the worm drive clamp at the y-pipe to cross over connection had worked itself loose and was just rattling around. Another possibility would be your air pump. The air pump engages and disengages depending on the load to prevent it from running at the high rpms. If that is the problem you should be able to pick one up for cheap off the forum. A lot of people remove them. Or just take it off and run a smaller belt and enjoy the extra hp.

 

Yeah, I thought I recalled the ISC being nearer the throttle body.
And, I have to run the airpump since I'm in a smog state.

Could over-tightening the belts affect the airpump's ability to engage/disengage?
I got them on there pretty snug.

 

Speaking generally, not rx7 specific, over tightened belts can cause noises from the pulleys. But that would be noticeable up front and not under the UIM. The air pump has an internal clutch that allows it to engage/disengage. If that is starting to go it would definitely cause some buzzing that would echo through the piping and be audible around the UIM. I can't say for certain belt tension would affect it's operation.

But a lot of auto parts stores like advanced auto have belt tension gauges for rent/use to get yourself in spec. Just call around and see if any stores near you have one. The FSM has the values for what a belt should be set at. It's a quick check and should be done any time you loosen or remove a belt. An overly tight belt or a loose belt are equally dangerous for an engine. You don't want that snapping on you on the highway.