Getting very low gas mileage/ rough idle
 

I mainly do city driving in my 90 turbo II, nothing with heavy traffic or anythin- just the odd redline from time to time and some very light traffic. Doesn't have any ports or anything- car is basically stock in terms of engine/turbo. It has a microtech, but I've NEVER heard of a microtech causing this much of a spike in fuel usage. A couple months a go it was tuned, and fixed some cold start issues. It uses a lot of gas, around 7-8 mpg, and I have no idea how its that bad!

Some symptoms I have no idea if related but might help nonetheless:
-when starting (which when cold takes a couple seconds to crank) often starts and then dies if I don't give it a little gas, sometimes even when slightly warm.
- Idle dips to about 700rpm for about 1 second sometimes, and comes back up. Does this every 5 seconds or sometimes more frequently.
- Power steering drops the rpms at a standstill to about 650 rpm
- a soft ticking noise that kinda sounds like a belt, comes from behind the dash, can only be heard when foot is off the gas pedal and car is at idle.
-cold start is very shaky
-car gives off strong gas smell as if the engine timing was retarded.

I am very doubtful of any compression issues, car has very solid power, and engine runs great when warm. I also just changed sparkplugs too. Could this just be a tuning issue?
Appreciate any help.

It doesn't matter if it is a Microtech or a Haltech or an Alabama Tech(football reference)....If you have a bad tune then your car will suck gas like a faucet.
..and if you have no experience tuning then that will tend to go hand and hand with bad gas mileage.
You should seek out a Tuner near you to go over the maps and perhaps fine tune your car.(dipping rpm sounds like a slight TPS adjustment is needed..BUT I am not a Tuner..I pay people to tune my car!..lol!)

I second the review of your tune. You could also have one or more injector issues. Timing isn’t my first suspect causing it to run rich.

I have crappy running Microtech cars brought to my shop all the time. Chances are that the car was never tuned in Matrix Mode. Which basically means that it was tuned for idle, 4000rpm and WOT, nothing between those areas. Some tuners like to call it a "drag race" tune, since it basically is not tuned for any other type of driving. Matrix allows tuning in 500rpm increments.

I can honestly say that in nearly 20 years I have never seen a car come into my shop that was switched to Matrix, regardless of who did the previous tune. Microtech is not a bad ECU as long as it is tuned correctly, same can be said for most ECUs.

normal mode still has maps leading up to 3500 RPMs, but yeah it's a lazy way to adjust the high end mapping, mostly relying on fuel pressure to remain 1-1 and the injector curve to be statically increasing. some cars it works well with and others show potential issues with the car in normal mode which sometimes you lose sight of as you continue your corrections while in matrix mode.

you can still get half decent results without matrix mode, but mostly a lot of tuners don't care about fuel economy for a 'tuner' car, why i do not know. mostly because it takes a bit of effort to tune the car to the ragged lean end out of boost that makes tuning the cruise portion so time consuming, it takes as long if not longer than tuning the top end because every transition from lean to tip in takes time to adjust otherwise the car will run like ass but get decent economy. people tend to complain more about the car hesitating than they do about getting poor economy. then on top of all that the tuner must add in proper corrections for seasonal changes.

mostly it's the fact that there's more bad tuners out there than good ones.

personally i start in normal mode, then i move to matrix mode, as well normal mode normalizes all maps from 4k and up prior to switching to matrix so it saves time and is one potential reason why it exists...

Correctly tuning a Microtech is very time consuming. Tuning WOT is easy, tuning the car so that it can be driven slowly through town is what takes a lot of time and skill.

I suggest you get yourself a wideband and a Microtech dongle (if you do not have one).

Idle oscillating (or car dying) is very much can be related to the car running too rich. A cold start tune two months ago may no longer be a proper tune two months later during the winter time. So while it is cold out there (I assume so) it might be a good time to double check/refine your tune. It's time consuming to get a well balanced cold start tune that is good for the whole year, but it's possible.

not to potentially burst the bubble but you may want to do a compression test also. low vacuum can cause a rich condition, rough idle and stalling. unless you have vacuum numbers and an AFR reading all we can do is guess.

you can verify the ticking noise by removing all the accessory belts, if the noise persists even with the belt off and it isn't obviously coming from the transmission then that is bad news. i have seen rotor faces balloon out and strike the rotor housing with each rotation and causing an audible tick, this also causes compression issues and some of the other symptoms listed. what causes this i have never quite determined, but i can only assume it was a lack of lubrication or severely overheated crankcase oil but i have seen it 2 times, and only on S5 engines.

another possibility is a loose exhaust port sleeve if internally from the engine, unfortunately no easy fix for that besides a teardown and proper repin of the sleeve. if this issue, leaving it be isn't wise as the sleeve will eventually loosen to the point that it catches exhaust gas and warps, mostly blocking the exhaust from that port.

Appreciate all the help guys. I'll get it tuned properly soon, and actually do a compression test (fingers crossed).
This is my first RX-7 so I really didn't know if being this bad on gas was normal or not lol.
With regards to the ticking noise, thanks insightful, that's a good weekend project for me.

Rotors never "balloon" out, they cave in.

https://cimg4.ibsrv.net/gimg/www.rx7...53b0e85be3.jpg

^ lol...agreed.

it DOES happen, just because you haven't seen it doesn't mean it doesn't exist. 2 in roughly 1000 or so examples is fairly rare.

unfortunately i do not think i took or saved any pictures of the examples i ran into. the denting due to detonation and high power is a totally different phenomenon.

i've also seen rotor housings with huge bubbles underneath the chrome, though that is usually either rust or delamination of the chrome near the spark plugs.

^Please explain the mechanism responsible for a ballooning rotor. I’ve never seen it either.

i already mentioned that i could not explain how it occurred, but it's funny that you both think i'm lying about it..

i might still have one of the rotors, if i find it i'll be sure to get a picture.

LOL. Literally mechanically impossible. Please explain what you think they are being inflated with. If you tell me oil, I will fall on the floor laughing and discount everything you ever have to say on this forum from this thread forward. Even 250psi of oil pressure would blow by the oil control seals before ever "inflating" a rotor. I have only called you out a small portion of your misinformation, but this is pure crap.

"Bubbled" (actually warped) rotor housings are from extreme overheating. Cracks around the spark plugs are from running too much boost with a plug that is too hot.

Rotors with contact marks are from worn bearings or e-shaft flex, not from inflation.

I have personally built well over a 1000 engines and pulled apart many more, there is NO WAY TO INFLATE A ROTOR!

“Soft ticking” sounds that change with rpm and car stationary can be a lot of things. First suspects would be a bad plug lead, belt or pulley issue or an exhaust leak somewhere. MAYBE an injector I suppose, but I’ve never heard them being that loud. The only thing I can think of related to the transmission that would make noise with the car stationary but running would be an input shaft or pilot shaft bearing. But that’s usually a growl or whining not a tick. And not from the dash area.

i mentioned i could not explain it, twice. but it happened, don't ask me how.

now you're just being an asshole.