'94 850 Turbo-Hesitation/Weak Accel. Under Light Throttle

IG-88A · Post by **IG-88A** » 23 Jul 2015, 17:21

Hello. I just started noticing this issue that usually seems to happen when the car is cold, when I'm just taking off. With the throttle at 1/4 or less, It'll seem like its starving for fuel and feels king of bogged down. If I leave the throttle exactly where its at, it will eventually catch up with itself and I'll get a sudden surge of power and all feels right again. If I increase throttle, it will correct itself, but it seems as though I have to push it a little more than I normally would. If it does the same thing once warm, I either haven't noticed it because it mellows out some, or it simply doesn't do it once warmed up. This has yet to be determined. This is always noticed when I first leave home in the morning, or leave work in the evening, or anywhere that the car hasn't been driven for a while. No codes except for EVAP.

Some things to consider. Plugs, wires, cap and rotor are all less that one year old, and are of recommended brands. Plugs were gapped correctly and double checked during a previous issue. Temp sensor and thermostat are less than one year old. IAC and TB were cleaned rigorously a little over a year ago along with new TB gasket. Vacuum tree and o-ring are new. New silicone turbo hoses a few months back, including silicone IAC hose. New FP Relay a few months ago. Can't detect an glaringly obvious vacuum leak by spraying aerosol.

I do currently have a split in my fuel tank at the seam behind the heat shield, hence the EVAP code. Not sure if this would contribute to this issue or not. Trying to to find a good used fuel tank is proving difficult.

Another piece of info is that my mileage in this car has always hovered around 20-21 avg. according to the computer. This is with mixed city/hwy. I realize its low. But I do have a recurring knock sensor code that I haven't ironed out yet that may be contributing to the poor mileage.

Any ideas would be appreciated. Thanks.

Post by **abscate** » 23 Jul 2015, 23:40

It could be a tired TUrbo control valve slow to give you boost, but that doesn't mesh with the cold/warm behaviour very well. We will have to noodle this one. I'm still betting on a vacuum leak or boost leak.

IG-88A · Post by **IG-88A** » 24 Jul 2015, 07:29

An odd occurrence on the way in to work today. Avg. mpg according to the computer has been hovering around 21 for the last six weeks or so, when i reset it. In fact, its always hovered around there since I bought the car. This morning after travelling maybe 1/2 mile, the avg. mpg was down in the 19s, then dropping into the low 18s when I was going up an entrance ramp. by the time I got to work it was right about 20, but it didn't hit 20 until I got on the highway. Had I done any more around town driving, I have a feeling I could have got the thing to read in the 15s. I was under the impression that after any decent length of time, in this case, six weeks, the avg. mpg won't fluctuate much because of the total log time involved. Longer time without a reset/less fluctuation in avg. mpg. I've never noticed it dip and raise like this before when avg. mpg was being displayed. When I selected real time mpg, and gave it enough throttle to get the factory turbo gauge up to about 3/4 or above, my real time mpg was sometimes in the single digits, at anywhere from 7-9 mpg. This was just normal passing or accelerating throttle. Not revving it hard or anything. Not sure if this opens up any possibilities or not. I've checked the boost hoses and connections. I can't check the lower IC hose at present because I lent my jack and ramps to a friend last weekend. Hoping to get them back tomorrow.

Sommerfeldt · Post by **Sommerfeldt** » 24 Jul 2015, 08:33

When I put my foot down, and during accelleration, my T5 does 4,7 mpg. That means nothing - it's the average that counts, and that number's fine. That six-week average you've got going shouldn't be taking momentary dips like that, though - that's very strange indeed.

Anyway, check that your WG isn't stuck. Mine was stuck half open all of a sudden, and boost pressure and MPG went in the toilet (the mpg probably b/c I was giving it more gas to try and keep up with the pressure flooding out the tailpipe...). A little wiggle and jiggle and it was back in business, and mpg back to normal (though a new actuator is probably coming up soon...). Just an idea.

- S

IG-88A · Post by **IG-88A** » 24 Jul 2015, 09:36

Thanks, Sommerfeldt. Just went out and checked. The wastegate actuator moves freely.

I was awfully puzzled by that average fluctuating, as I'd never seen it do that before.

So the 21 avg. is fine? I'd seen reports of normal averages ranging from 24-26 mixed driving. But maybe they were babying it. I don't stomp it all the time, but I don't grandma it either.

Sommerfeldt · Post by **Sommerfeldt** » 24 Jul 2015, 14:27

I get about 26 mixed, and I don't baby mine at all. I've got a big-ass K&N sport filter in there, and I love hearing the turbo.

That said, a 21 isn't bad for a '94 Turbo. Make sure it's breathing freely and your stage 0 is done, and you might be able to get it higher. Also, I recommend samco hoses - may be my imagination, but they seem to have helped with mpg on my 850s.

- S

IG-88A · Post by **IG-88A** » 24 Jul 2015, 16:35

I've got the Mishimoto ones, so probably the same difference. Of course, I do have this knock sensor DTC that keeps appearing, and from what I understand, that particular code will cause rich running conditions. That could really be helping the less than stellar mileage as well. I've tried cleaning the old sensors and connectors, just haven't tried the new sensor kit yet. I'm really trying to get to stage 0, but I'd have an easier time of it if things didn't keep popping up, haha.

I'm going to dig around in it this weekend in the blistering heat, and see what I can find. Hopefully something jumps out at me.

Thanks for the replies.

Lost240 · Post by **Lost240** » 04 Aug 2015, 13:12

Did you find anything out on this? Mine has a very similar issue. I have completed all of Stage 0. This weekend I even cleaned the MAF and throttle body which didn't do anything to help or hurt the situation. The car idles rough when cold and when i press the gas lightly it doesn't seem to want to catch to get started for a half second or so. When it warms up it is fine from a stop. However, I have some strange nonlinear acceleration issues.

Scholz · Post by **Scholz** » 04 Aug 2015, 15:44

Have you had a look at your fuel trim adaptations?

kauboi · Post by **kauboi** » 04 Aug 2015, 18:49

I'm an 850 noob, but my car acted like you describe before and after I did a complete tune up/vacuum hose replacement on my newly aquired 850R.It passed smog, and was smooth, so I chalked it's tired sluggishness up to mileage (210k). One day, I removed the throttle cable at the TB and held it up vertically and shot penetrating oil in it a few times. Different car after that, and for me a total D'oh! moment.