Flat spot - help!!!
 

I'm in England and my '96 59k miler is on it's 3rd MAF with a standard air filter.

It has a flat spot (half power, stutters like choked) between 1,800 rpm and 2,400 rpm. After that, it's amazing - pulls like a train. Oh, and it's fine when cold, flat torque curve, smooth as silk.

It's on it's second brand new MAF from Subaru but they last 1/2 a day and then show up code 23 and the car runs like a moped. Any ideas anyone? There are only about 35 RHD left in the Uk so no-one has a clue here.....I'm at my wits end as the rev range is exactly where the car sits in normal urban traffic and I am being overtaken by cyclists going up hill - the shame.......

Re: Flat spot - help!!!
 

That's seriously bad news Roger.

I have two or three UK models here in Ireland.

They are hard to diagnose, and you need somebody who is good with Subarus to work on them. They are not THAT difficult to work on, after all they are just an Impreza really with 1.5 engines and without the complexity of the turbos. :rolleyes:

It sounds like the MAF is not your problem. Code 23 merely says "abnormal voltage from MAF sensor circuit" If you have replaced with a brand new good MAF and you still have the same symptoms it's likely the problem was elsewhere all along. Please don't throw away the old MAF, it may be OK.

What's happening is the ECU is seeing incorrect voltages from the MAF circuit and it is defaulting to a get-you-home fuel map known as limp home mode. When the voltage reverts to normal or what the ECU "expects" to see, then she will run sweet.

What's likely to be faulty is a bad connection in the loom between the MAF and the ECU, or worst case scenario the ECU itself could be damaged or faulty. However, don't panic yet. We can check everything else first before we throw money at replacing ECUs.

Do you have access to a Work Shop Manual? If not I can scan the two pages for you and you could get a competent fuel injection auto electrician to check out the voltages and the harness continuity for you. I'm guessing you merely have a bad connection somewhere.

Joe :)

Re: Flat spot - help!!!
 

Could this very well be a throttle position sensor issue? My car was experiencing this affect yesterday and with light constant acceleration, somewhere near 2000 rpms, the car bogged down as if gasping for air and losing power. No codes were shown.
Later that night I adjusted to near .50Vdc on the sensor and the problem was reduced greatly when I drove today.
I'm just curious if these problems are related to the proper setting on the TPS.

Re: Flat spot - help!!!
 

That is more than possible Matt.

However Roger is saying his is throwing code 23 repeatedly. TPS code is Code 31.

It would still be wise to set the TPS voltage as you say. The TPS rheostat tends to wear out in the position of normal driving. In the SVX because of the auto gearbox steady state driving keeps the TPS almost permanently in the one position, with subsequent wear.

Joe

Re: Flat spot - help!!!
 

Hi people, thanks for the replies and whew, glad to have someone else out there that I can talk to. I'm not alone then :):)

The guys who are working on the car know Subaru's fairly well and their next suggestion was to pin out the loom between the MAF and the ECU to check for resistance or voltage drop. Joe, essentially, this is what you are saying, yes? No, I don't have a manual and if you could spare the time to scan a couple of pages, my email is roger.stephens (at) me.com - I'd be really grateful, thank you.

I intend to keep this car for as long as a) it will keep going and b) I'm still alive :) I've had about 50 cars over my lifetime (50 now) and this has to be the most fun as a daily driver I've ever had. And for no money!!! These cars are SO undervalued.

Again, thanks for your help - I'll let you know how it goes!

Re: Flat spot - help!!!
 

Now just noticed something strange. If I go out and hammer the car for 1/2 hour, ie max revs on throttle kickdown, 10 mins at 90-100mph (allegedly - not really) and generally kick the sh*t out of the engine, for 1/2 hour, it's a sweet as a sweet thing :) But then 1/2 hour later, it goes back to being a granny car at the same old revs. Would that more likely indicate an ECU fault? Just guessing here cos people like Joe and Matt have clearly much more understanding than I do! Cheers, Roger :eek:

Re: Flat spot - help!!!
 

No one has mentioned the IRIS valve yet. Do a search on that and see if that might correlate with your symptoms.

Re: Flat spot - help!!!
 

Good suggestion and I will ask SMD to have a look at it. But as I understand it, the IRIS valve opens at 4,000 rpm and closes below that. i don't think it would osscilate at the 2,000 rpm mark. But. The gearbox TCU shuts down one bank of the 6 cyls on full power shift temporarily to ensure no jerks in full power shifts and maybe it uses the IRIS valve for that? Curioser and curioser :) Thanks for the suggestion, much appreciated.

Re: Flat spot - help!!!
 

My understanding (if you can call it an understanding, since I only vaguely remember some possibly innacurate information) is that it does something at 2200 rpms and then again at 4000 something rpms.

Re: Flat spot - help!!!
 

The IRIS closes at 2200 to form the Inerta system, opens at 4000 to form the Resonate system.
If it does not close it will lack torque below 4000.

Harvey.

Re: Flat spot - help!!!
 

Hi Roger

I've just sent the scans to your email. If they don't arrive let me know and I'll publish them here on the web and you can download.

Joe :)

Re: Flat spot - help!!!
 

I think I'm experiencing something like Roger now, but not sure what this is...I'm thinking faulty IRIS because I got it used from someone I don't trust at all on this forum.

Here's what my car is doing lately....Applying light constant throttle after sitting at idle..the rpms will increase and at about 1750rpm to 2000rpm (sometimes) the car will bog down and have no response. I mashed the gas twice when this happened and no response at all...very weird...The 3rd time I mashed the gas, the car responded.

I have no codes displayed, the TPS is adjusted as well. Something is causing the car to delay response.