salewit Posted June 28, 2008 Share Posted June 28, 2008 92 Legacy. Car bucks or surges in ALL conditions except heavy acceleration. Doesn't matter if engine is cold or hot. From idle to highway speed. Most noticeable when steady on the pedal at about 30MPH it'll surge then hesitate. Problem seems to be getting worse. At idle, my tach will sit at about 800RPM, then all of the sudden the engine will shudder for about 3 seconds and the RPM dips to 400-500, then other times it will race up to 1500 RPM. Hot or cold. I've done a lot of searching here and found LOTS of people with the same situation. The problem is everyone has a different "opinion" on what is wrong. I've read injectors, fuel pump, MAF sensor, temperature sensor, plugs, wires, coil, O2 sensor, crank sensor, etc. I don't have the money to just change things left and right and some things I changed a few months ago during a different problem (failed smog). I'm wondering if anyone can recommend a sequence of things to diagnose to help me find out what the problem is. I've recently changed: Plugs, PVC, air filter, fuel filter, oil and filter. Approximately 3-6 months ago I replaced: cam sensor, temperature sensor, O2 sensor and visually inspected inside of catalyic convertor, tested throttle position sensor with ohmeter. Thanks Quote Link to comment Share on other sites More sharing options...
EVOthis Posted June 29, 2008 Share Posted June 29, 2008 not that im any good on diag. but i will do the best i can here..(im sure others will chime in later) is there any CEL on?.... automatic or manual trans?.... have you tried cleaning your IAC valve? Quote Link to comment Share on other sites More sharing options...
Manarius Posted June 29, 2008 Share Posted June 29, 2008 MAF sensor. That's EXACTLY what my 1991 Legacy did when the MAF was shot. My suggestion is that you swap it with a known good MAF so that you can test whether the MAF is broken. Quote Link to comment Share on other sites More sharing options...
OB99W Posted June 29, 2008 Share Posted June 29, 2008 The reason there are so many "opinions" is that there are many causes of surging. That's especially true with modern engine management systems. The ECU monitors and controls several things, and attempts to correct "out-of-limits" operation. Unfortunately, sometimes sensor data lags too much and the compensation is excessive -- eventually the ECU senses the overcorrection, and then pushes too far in the opposite direction. Also, some faults are beyond the ECU's ability to compensate for. The basic requirements for an engine to run are all potential sources of surging and/or hesitation as well. (I'll leave out the things you've recently replaced, although there's no guaranty one of them isn't the culprit.) Air -- vacuum leaks are a common cause Fuel -- fuel pump, fuel pressure regulator, injectors Spark -- coil, plugs, wires, but they don't tend to improve under "heavy acceleration" Compression -- valve issues, possibly related to... ...Timing (belt) -- a one or two tooth mistiming can play havoc with things. Is this the engine that last year had such a problem? If so, I seem to remember that at the time, all that was done was retiming with a new belt, but no replacement of tensioner, pulleys, etc. Perhaps it jumped (again?). Sensors -- yes, you replaced some, but there are others. Quote Link to comment Share on other sites More sharing options...
four-fleet-feet Posted June 29, 2008 Share Posted June 29, 2008 92 Legacy. Car bucks or surges in ALL conditions except heavy acceleration. (failed smog). OK, those are words I've dealt with in the past. You just described my old S-10's last year on this Earth to the T. Did you get the car scoped afterwards for a diagnostic? What exactly did you fail on and what did you fix to pass? FYI: you can have a problem and still marginally pass. BTDT. If you didn't get it scoped, here's what was wrong with my truck; you could check all of these items. First, I already had new plugs, gapped correctly. Then I found a vacuum leak. Found a cracked hose, fixed it by stripping a junker or two of all vac lines (and had a pocketful of spare emissions items just in case) for about $20. Then I started getting EGR CEL codes. Replaced it. (Actually needed a new EGR GASKET because one of the vac leaks was from it, replaced just the gasket and passed, but the surge was still there. Since the thing was a bear to diagnose, finally just pulled the whole EGR and threw a 'new' JY one with another new gasket on.) Finally needed to get new plug wires (needed a cap wire but no singles were to be found - distributor engine) and a new (ha-JY) TPS. The problem was then fixed; what I'd actually gotten was a cascade of failures from that cracked vac line. I passed when I fixed the EGR gasket, but my truck ran like crap. Until I found EVERYTHING broken, it wouldn't idle and surged at its own pleasure. Drove me nuts. So, go back and check everything. If you didn't use NGK plugs or OEM wires, you might change them. If you aren't exactly sure you have the correct wire to the correct plug (hey, it happens), check them all. It took a lot of time to figure out what might have been wrong with my truck, and aircraft-engineer and I were at wit's end (and wasted a lot of time) until we paid $95 to get it diagnosed. Then we fixed it in about 2 days, once we found donor trucks. It was worth every penny to finally find out everything that was really wrong! If you can't remember (or find the paperwork) what made you fail emissions, it might be worth it to get this diagnosed by a shop. Then you can fix it yourself. But you can't fix it unless you really know what's wrong! Quote Link to comment Share on other sites More sharing options...
salewit Posted July 2, 2008 Author Share Posted July 2, 2008 ...Timing (belt) -- a one or two tooth mistiming can play havoc with things. Is this the engine that last year had such a problem? If so, I seem to remember that at the time, all that was done was retiming with a new belt, but no replacement of tensioner, pulleys, etc. Perhaps it jumped (again?). Yes that's me again! Actually this is the first thing I checked when this problem started getting worse. The valve timing is right on. On the plus side I can now get to my timing belt in about 7 minutes flat! What's weird is when I changed all the basic "tune-up" things noted above, the car smoothed out considerably... for a few days... and then went back to its bad habits. Getting worse almost daily. But absolutely no problem with heavy acceleration or climbing hills. Doesn't miss a beat. I haven't had any new CEL messages since I cleared it during my smog fiasco last year. The smog test numbers from what I remember were excellent once the O2 sensor wires were connected properly. The car wasn't scoped. Manual transmission. Can't find my book.... what and where is the IAC valve? I'd love to try swapping out the MAF sensor, but that's a $300 gamble. Is there any way to test the sensor with a multimeter? The plugs I used I think were NGK gapped to .044". As far as getting it diagnosed at a shop... I know I'm being stubborn, but I just have such a bad taste in my mouth from the shop I took it to during my bad smog test that diagnosed it as a bad cat. It turned out to be the sensor connected improperly. This shop was very highly recommended... Valuestar and all that. Not saying that this is a smart move for me to be fumbling around here, but I suspect a lot of you know where I'm coming from on this. Kind of like going to a prostitute. Quote Link to comment Share on other sites More sharing options...
wtdash Posted July 2, 2008 Share Posted July 2, 2008 Oakland must have a pull-a-part? Get a MAF for cheap and if it doesn't work take it back. Good luck. Quote Link to comment Share on other sites More sharing options...
montana105 Posted July 2, 2008 Share Posted July 2, 2008 were all the jobs done in response to the engine running crudy or did it appear after doing normal maintenance stuff? Quote Link to comment Share on other sites More sharing options...
salewit Posted July 3, 2008 Author Share Posted July 3, 2008 were all the jobs done in response to the engine running crudy or did it appearafter doing normal maintenance stuff? Yeah they were done post crudiness. Oakland must have a pull-a-part? Get a MAF for cheap and if it doesn't work take it back. Sure there's junkyards all over, but I didn't think they'd ever take a part back. Especially an electrical part. But I'll check it out. Quote Link to comment Share on other sites More sharing options...
OB99W Posted July 3, 2008 Share Posted July 3, 2008 What's weird is when I changed all the basic "tune-up" things noted above, the car smoothed out considerably... for a few days... and then went back to its bad habits. Getting worse almost daily.It may not be all that "weird". In the process of working on things, it's possible to disturb connections, etc. For example, if something isn't making good contact due to corrosion, even slightly moving the wiring/connector might "fix" it for a while. But absolutely no problem with heavy acceleration or climbing hills. Doesn't miss a beat.[...] I'd love to try swapping out the MAF sensor, but that's a $300 gamble. Is there any way to test the sensor with a multimeter?[...] Next time it's acting up at idle, try tapping on the MAF and wiggling the wiring to it, and see if there are any changes. If the MAF is contaminated, it can often be cleaned (carefully -- they're fragile). The following links have good info.http://www.babcox.com/editorial/ic/ic110034.htm http://endwrench.com/images/pdfs/EWMAFAug05.pdf Quote Link to comment Share on other sites More sharing options...
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