kosis

Hello everybody, new guy to the forums here. Thought I'd see if anyone had any experience with a similar problem. I don't know too much about cars, and the mechanic I usually go to for fixes isn't sure what the issue is (his specialty is not Lexus).

Out of nowhere a couple of weeks ago my car decided not to start. It would engage, turn over, but would start hiccuping and turn off after a few seconds. I tried a few times in succession with the same thing happening.

My mechanic came by and assumed it was the fuel pump. He opened some sort of valve by the engine, asked me to turn the key, and fuel squirted out. He told me that this meant the fuel pump was OK because it had no problem getting to the engine. He then changed the spark plugs in my engine. No difference. Finally he tells me that it may be the mass air flow sensor but it's an expensive part to buy just for guessing and testing reasons. Says he did his best because he doesn't have any diagnostics computer for a '94 Lexus.

Long story short, I get the sensor off of ebay, replaced it, and the same issue happened. So it's not the mass air flow sensor.

Here's the thing though.... after starting it multiple times one day and getting it to idle, I slowly hit the gas and let go every time it began to hiccup. After about 30 minutes of this I realized that I could get it to drive. I could drive it at about 10 mph max for a couple minutes before it would hiccup and turn off/get close to turning off. After an additional 15 minutes of idling or driving slow, I was up to 35mph.

I drove it around to keep the engine hot, went to the store for 15 minutes, came back and it started up normal. Let it cool for a couple hours at a friend's house, started it up and got it to go... though it started showing similar signs again at about 25mph. After resting it overnight I was at square one. If I let idle for a while and gradually hit the gas I can get it back to regular working conditions.

My question of course is this. What could possibly be the issue with this car? It runs like normal only when the engine is hot. Anybody have this experience before?

I know I'm new to the forums and this may be a new jack question but I was hoping someone had some expertise they'd be willing to share. Sorry for the long post but I tried to be as clear as possible.

Thanks in advance!

GEORGE_JET

The 94 is OBDII so you should be able to get codes read at most auto part stores, start with that (even if the light is not presently on). Checking to see if fuel sprays out of a valve in the engine is not going to tell you if the pump is good, you need to check it out better than that. Ideally you should get a fuel pressure checker and see exactly what the PSI is.
Have you checked all the hoses underneath the hood for cracks and splits? Also check the fuel filter, see if it is clogged.

kosis

Thank you for your advice. Problem is I don't think it is in fact OBDII. I've been told by numerous people that it's not, including mechanics and Autozone. No cracks or splits that anyone could see.

My mechanic felt confident it wasn't the fuel pump but I will look into a fuel pressure checker. Thanks again.

Keep the suggestions coming.

GEORGE_JET

You can check the drivers door sticker, it will tell you the month and year the car was built. It may be early enough in 93 that you do have OBDI (they start building 94's late in the previous year, and some to not have all the mods). But chances are it is OBDII. Toyota and lexus made the switch before most other manufactures. Have you found the diagnostic connector? That will tell you the final word for sure. If it is OBDI, you can use a paper clip to check for codes (the clip will put OBDI into diagnostic mode and will then flash the check engine light). On these types of drivability problems, checking for codes (even if the light is not on), is a excellent place to start.

kosis

My friend, you have been a huge help. Turns out that it is OBDII after all. For whatever reason nobody I had asked for help had known this. Because you mentioned it I did a little research and found out what the input looks like... and sure enough you were right.

I then went to back to Autozone to explain. He was frankly a bit embarrassed that he didn't know. He checked it and came up with a faulty Cam Position Sensor. Seems to make sense when he explained what it does. Hopefully I am on the road to recovery. I can't thank you enough George!

GEORGE_JET

Glad to hear that I was able to help clear this up for you. What was the code number that he pulled up?

MikeLex

^ George_Jet is absolutely right about that. It's most likely you have a cam position sensor not feeding the ECM during cranking. A new sensor costs about 100 bucks so try to find an used one in good working condition at the nearest junkyard, replace your old unity and see if you get the problem fixed. The cam position sensor is located in front of the engine (i.e. close to the radiator) a little below the oil fill hole. The replacement is almost plug and play.

kosis

The trouble code is p0340. I see that it includes open circuits as well as other potential problems to go with the cam position sensor possibility. Tomorrow I'm picking up the sensor from a used spot and hoping that does the trick.

Thanks for the location Mike. You saved me from what I thought would be a scavenger hunt trying to find the thing.

kosis

Update: Installed the Cam position sensor and the same problem persisted. At least I know the proximity of the problem? For others with the p0340 trouble code, what was the culprit? Faulty wires?

renatodato

Check the connector to the CPS. These connectors are known to get corroded if the CPS leaks oil into the wires. I went to my local junkyard and got this connector which I soldered. You can check for voltage with a multimeter too. If the connector is full of oil, chances are it has very little current going through it.

kosis

Thanks renatodato.

I actually had Lexus diagnose it for me and they uncovered that it's the Idle Air Control Motor that is gunked up and causing the difficult start up. Turns out when the engine gets hot, the oil/gunk starts melting and allows for smooth driving. Sounds logical enough. They want me to replace it but word on the street is that I should be able to clean it. We'll see what happens. Keep this in mind if anyone has similar problems.

Thanks Lex fam.

MikeLex

A new IAC valve costs about 250.00, so think twice before replacing it. I wish I could trust on the dealer's mechanics, but... To me a bad IAC valve would cause evident idle speed issues (low, fast, bad), not an intermittent engine running problem. Also, did you ask them why the ECM stored a P0340 code?

GEORGE_JET

I really do not like the sound of this. How does the car run off idle? Say driving down the road / freeway? Do you have good power? with no symptoms? If it runs well at cruising speeds, I would suggest clearing the codes and then cleaning the IAC motor.

Idle air control problems will only be evident at idle, and low speeds, not while crusing. And it has nothing to do with the error code that you have

kosis

Thanks for the replies guys.

My problem persists.

A friend with a bit of car know-how and I removed and cleaned the IAC and put it back in. This morning I had the same symptoms. My problems only exist when the engine isn't warm/hot from running.

The technician at Lexus told me I had a bad IAC and they'd replace it for $466. Obviously I don't want to pay that so I decline the service and search the net. I read that in many cases the problem with the IAC can be remedied with cleaning, but obviously that turns out not to be the case with mine. He also told me that even though this problem is caused by the IAC, my check engine light is due to other issues. This I know because the check engine light has been on for years. I told him all I was worried about right now is the issue with start-up, to which he told me it was definitely the IAC.

Again, the check engine light has been on for years and never had engine related issues with the car that I was aware of. A mechanic told me he didn't feel there were any major issues either, especially for a car made in '94. Earlier in the thread, before I went to Lexus, I figured the codes would solve the problem. Again, the p0340 code popped up which pointed to the cam position sensor. This was replaced but didn't fix anything. Luckily I was able to return it. It was at this point that I figured I'd pay Lexus to make the diagnosis and get it fixed for cheaper at a mechanic. So this is where I stand.

In my opinion, the IAC must be faulty. If Lexus was so confident this was the issue, could they have replaced it and still charged me if the problem wasn't fixed? I never told them the cam position sensor was a red flag and they never brought it up. I guess I'm just thinking that since they went into the problem blind and confidently found the IAC to be the culprit, it probably is. Am I being naive?

Here's how the car runs to be more specific:

-First thing in the morning when I start my car, it turns on, then begins shaking/sputtering for a couple seconds and turns off. I repeat this a few times.

-After 5-10 tries, the car will stay on in idle. I let it sit for a few minutes, engine running.

-Parked, I give it gas and get it to about 1 rpm before it starts shaking/sputtering so I let go to keep the car running. Wait another 5 minutes. I now can get it to about 2.5 rpm before the shaking/sputtering.

This is enough for me to drive around my neighborhood (25-40mph). Once I'm on the road at this speed I see no problems whatsoever. It drives like new. Now that the engine is hot, it's as if I have no problems. I can turn off and start the car effortlessly. The Lexus technician described what was happening as the gunk/grime in my IAC being freed up/melted because of the hot engine.

If the car is then turned off for a couple of hours, it still starts fine but starts sputtering again around 2 rpm. All I do is stay a little bit under, drive for a few minutes and can get it back to over 2.5 again. It's very obviously a problem related to the engine being hot/cold so shouldn't this narrow the problems down?

Any other tests I should try? I'm wondering if the diagnosed p0340 code was triggered years ago and turned the check engine light on and has nothing to do with this start-up issue. Either way, the cam position sensor replacement did nothing. Cleaning the IAC now did nothing. What are my remaining options? I don't want to get a new IAC but i'm not sure what else to try.

Thanks again for all of your help.

GEORGE_JET

Ideally at this point it would be a good idea to scope both the crank and cam signals, but you probably do not have access to a scope. Check your fuel filter, Then clean your MAF sensor (they have cleaner at the auto part stores specifically for cleaning MAF). If this does not help your problem, find ANOTHER mechanic. The LEXUS dealer is giving advice. They may possibly get this fixed. but not before several trys, and it will be very expensive.