Vegan Posted April 29, 2014 Posted April 29, 2014 94 ls400. Changed plugs, wires, both coils, distributor caps and rotors, cleaned throttle body. IAC is a type that can't be taken apart to clean, but cleaned what I could. Ran great for a day and then original problem came back: loss of power for a second at a time with combined engine light and drop in rpm. Happens at idle or full throttle. If you let it idle longer than a minute the engine eventually cuts off. If you keep driving the engine lights stays constant and constant restricted acceleration (as opposed to the power loss for a second here and there). RPM won't go above 1800. Can gradually get up to about 50 mph, but extremely sluggish when accelerating from idle. Has no codes. Fuel pump/regulator/MAF?
billydpowell Posted April 29, 2014 Posted April 29, 2014 this is what I would do, go get a used IAC (salvage yard) and put it on and see what happens.
fsuguy Posted May 4, 2014 Posted May 4, 2014 Hi, If your coils and fuel supply are fine, and you have no acceleration, it may just possibly be the Throttle Position Sensor (TPS). Look up any posts on this and you may find some suggestions. I had a similar problem with my '92 and changing the TPS resolved it. For really good and detailed instructions, look up the lexls site. Good luck!
landar Posted May 4, 2014 Posted May 4, 2014 I am not sure why you would have no codes especially if the 'engine lights' are constantly on. You should be aware of the infamous failing capacitors in the ECU's of this vintage of car. That would make the ECU act very strange and perhaps no codes. If it were my car, I would figure out a way to hook a fuel gauge to the rail such that it could be safely monitored while the engine is running. If it stays in the 45 to 50 PSI range, you can eliminate the fuel supply as a suspect and go after ignition. I would certainly encourage you to recheck for codes as that could be very revealing. Just double-check that you are performing the procedure correctly -> http://www.lexls.com/tutorials/intro/codereading.html
Vegan Posted May 4, 2014 Author Posted May 4, 2014 Two cans of seafoam fixed it. Put some in gas, some in oil, and sprayed a whole can in iac port and throttle with engine running. Now it's perfect. Thanks for the help.
Vegan Posted May 12, 2014 Author Posted May 12, 2014 Drove great for a week and then came back. Engine light and barely accelerates. Swapped IAC and no change. No codes. Have to put it in low gear to even move.
Vegan Posted May 13, 2014 Author Posted May 13, 2014 Changed the tps and adjusted it today. Car doesn't move.
landar Posted May 13, 2014 Posted May 13, 2014 I really would like to help you Brian but my suggestions generally are not heeded. I really did not see how the Seafoam was going to do anything but held my tongue. I think sha4000 suspected that as well. This type of problem needs a logical method of attack or you will be throwing money at things that will not fix the root problem. Get the problem divided into fuel delivery or ignition. Then go from there. Will the engine rev in Park? If so, that suggests that the engine will not handle a load but otherwise will respond.
Vegan Posted May 14, 2014 Author Posted May 14, 2014 Readjusted TPS today, but still has a very rough idle. Revs fine in park, but once in drive almost nothing. Narrow it down to the car, or not the car, and then go from there.
landar Posted May 14, 2014 Posted May 14, 2014 Funny Brian. I think we have narrowed it down to the car. Maybe take the gas cap off and put it on another LS and call it a day? I get your sarcasm. So, if the engine will rev while in park (no load to speak off) but begins to sputter and run rough when in gear, that *might* suggest fuel starvation. Might. A simple test could help. If you were to add some fuel while it was sputtering and it began to recover, that would lend support for lack of fuel. I have taken a can of starter fluid before and spritzed a little into the throttle body and gotten some clues. Of course you will need a helper and be very cautious but it can provide some insight. If the engine sputters and stumbles even more, then its not fuel delivery. Probably ignition. But if it does help a little then it is probably fuel pump, filter, etc.
Vegan Posted May 14, 2014 Author Posted May 14, 2014 It doesn't even idle at this point. Tried to test for codes again and didn't even get the constant blink. Starting to think it's a losing battle with possible bad ecu. I fixed the instrument cluster with radio shack capicitors and think I will do the ecu's, but with appropriate caps....to be continued, if I don't burn it.
sha4000 Posted May 17, 2014 Posted May 17, 2014 Don't burn it lol. I know it seems like too much at times but just work through your progressions of diagnosis eliminating one thing at a time. Landar was correct that I did not think the seafoam would fix your issue but I waited for you to report back on your long term reliability of that method. Just keep reporting back with what your doing to eliminate possible causes and I'm sure we will get it straightened out. Sometimes these things take a very long time for DIYers because of the lack of diagnostic tools though.
Vegan Posted May 18, 2014 Author Posted May 18, 2014 Found leaking cap on ecu. Ordered new ones via digikey. In the meantime, got a mountain bike on craigslist to get to work. At first one of the wheels was making a squeek sound, but sprayed some seafoam on it and its back to normal.
landar Posted May 18, 2014 Posted May 18, 2014 You could probably just seafoam the capacitors and they will be back to normal.
sha4000 Posted May 19, 2014 Posted May 19, 2014 Glad your on the way to figuring things out. Seafoam makes everything better lol.
Vegan Posted May 24, 2014 Author Posted May 24, 2014 Replaced caps, op check good. AC even works again.
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