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Have an intermittent hard start problem when it's warm; most noticeable when running errands and making 3 or 4 stops. Car will fire, but will take several times before it will finally catch... it will "chug" for 15-20 seconds before the idle will rev up to 1300-1500 rpm and then it will settle down. On some occasions will have to let it set for 20-30 minutes before it will start.

Did some research on this and other forums, and the FPR seemed to be a common cause for this. I did the test, leaving the vacuum line unattached for a good 5 minutes, no fuel, but replaced it anyways. Still had issues, so took it to my trusted local mechanic and he said it needed both the UIM and LIM gaskets. Picked it up and did it myself with the help of some you tube videos and the DIY on this site.

Definitely needed both gaskets and a new UIM; UIM was melted and was leaking oil into the LIM as well as outside the engine. Finished the job Sunday and have been driving it around, does run smoother and no burning oil smell. . However, stopped at the grocery store after a 30 min highway ride from home, got back in after 20 min and it was doing the exact same thing.

So now I'm stumped. If I had to guess, it is getting too much fuel/rich mixture; it is intermittent -doesn't do it all the time. What should i check/test? CEL is off.

When it's hard starting, try and check for spark. It could possibly be a bad crank sensor or ICM causing this, as both can give you issues when they get warmed up. Also you could try and clean your IAC and throttle body.

Another thing you can try to test the crank sensor is to spray it down with a garden hose when the hard starting is apparent, and pack the electrical connector with some dielectric grease. Sometimes the connector gets dirty and will give you starting issues like you're describing. Also, check your fuel pressure when it's hard to start as well.

I know this is kinda an old thread...but it took me this long to figure it out. Took it to my local indy, and said it needed an UIM and LIM gaskets. Decided to do it myself with the help of this forum and youtube. It definitely needed both, UIM was melted @ the egr tube and oil was leaking all in the top of the LIM ...probably 1/2 qt easy. However, this didn't solve the problem (although it did run smoother and mpg went up by 2 mpg). Cleaned the IAC, MAF and TPS still no effect. So at this point I had:

- swapped coil packs
- replaced FPR
- replaced UIM and LIM gaskets as well as UIM itself.
- cleaned the trio of sensors at the throttle body.


It wasn't throwing any codes, however, I decided to replace the IAC yesterday...seems like this fixed it. Starts quicker even when cold and doesn't 'chug' when restarting warm. Will probably take a few more times out to be sure, but the signs are pointing in the right direction...have my fingers crossed.

I guess I got my hopes up too much. Any suggestions as far as diagnosis, would be appreciated. recap of the symptoms:

- hard start warm, most prominent if i wait 15-20 minutes...sometimes won't start at all and have to let it cool down for another 20 minutes.
- pushing the pedal all the way to the floor does not help the starting process...makes it worse
- when it does start it will 'chug' with an oscillating idle until it 'clears its throat' takes about 10-15 seconds.
- SES light is not on.

This is what i have done so far:

- swapped coil packs
- replaced FPR
- replaced UIM and LIM gaskets as well as UIM itself.
- cleaned the trio of sensors at the throttle body.
- Replaced IAC

Jfridge92 wrote:When it's hard starting, try and check for spark. It could possibly be a bad crank sensor or ICM causing this, as both can give you issues when they get warmed up.

do you mean simply pulling out a plug and grounding it to see if spark is generated, or is there a more sophisticated test?

Also you could try and clean your IAC and throttle body.

Did this, and replaced the IAC.

Another thing you can try to test the crank sensor is to spray it down with a garden hose

It's 27 degrees here in the D' ... not feasible until it warms up.

Also, check your fuel pressure when it's hard to start as well.

If I've replaced the FPR, what part of the fuel delivery system can be affected by engine operating temps and only is an issue during starting? I've got a pressure gauge, so checking this won't be a problem....just trying to understand the logic so if i do get some funky numbers i know where to check next.

Any guidance would be appreciated.

Another simple test you can do is unplug the ECT when it is having problems starting, it controls the fuel delivery for given engine temps. I had a similar problem but mine would do it when it was cold. I believe another member had the same problem your experiencing when warm and his solution also was the ECT.

^^ I will try this. Interesting you mentioned it....when I did the manifold gaskets I bought a new one to replace as a PM measure (I also did the T-stat, as it appeared to be sticking based on T-gauge readings). The new one was DOA - As soon as I turned on the car it immediately pegged the meter at 260. I cleaned the old one up and put it back in and all was good.

Did you have normal Temp readings when it was acting up?

yes i did, there are two sensors, one for the guage reading and the other is for the computer to adjust fuel. The one im refering to is kind of just below the throttle body IIRC. And other than having starting problems it ran great.

I had the same issue on my 95 and it was the crank sensor.
I also had the issue that it would die occasionally while driving.
No sputtering or rough running, just ka-plunk die. Scary.

I don't really know how you can properly diagnose if it's the crank sensor
before you replace it. I just bit the bullet and replaced it because I couldn't
find any other plausible cause for the symptoms. It's not a fun job.

trf_ssei wrote:yes i did, there are two sensors, one for the guage reading and the other is for the computer to adjust fuel. The one im refering to is kind of just below the throttle body IIRC. And other than having starting problems it ran great.

There's two? The one that gave me the bad temp gauge reading is located about where you describe above... screws into the aluminum LIM towards the front of the car, just to the right (from driver's orientation, left if you are under the hood) of the T-stat. Is this the one you are referring to?

@skregal ... you are correct...neither part is very expensive (crank sensor or temp sensor) and I should swap out just to rule them out...just hate throwing parts at a problem vs. knowing for sure.

Heres a link to a similar problem i told you about.

http://www.pontiacbonnevilleclub.com/fo ... 16824.html

Yes that is the sensor i was refering to, next time you have the problem just unplug it and try to start the engine, if it still doesn't fire then you need to check for fuel and spark. Theres lots of info on here how to go about this. I was sure that the sensor i described to you was for the computer reading. What year is your car..? Mine was a 98 not sure if they did things different on earlier years.

Still having issues....

This is an updated list of what i have done so far:

- swapped coil packs
- replaced FPR
- replaced UIM and LIM gaskets as well as UIM itself.
- cleaned the trio of sensors at the throttle body.
- Replaced IAC
- replaced plugs
- Replaced crankshaft sensor
- swapped the engine control module (part that the coil packs sit on) with a spare used one

Still have the exact same symptoms....once it is really warmed up, will start for the first 15 minutes after shut off, then won't start unless you let it cool down for about another 30-40 minutes. Engine cranks freely. from what I've read about the only thing left is the temp sensor.

I have a new coolant temp sensor which I have yet to install...is there more than just the one that screws into the LIM located on the front towards the driver's side?

It still sounds like the CPS or the wiring to it. Have you checked for spark or fuel pressure when this occurs?

I know the ICM can be troublesome sometimes if it's going bad. They usually show problems when the car warms up, but typically they cause stalling or misfires, but hardstarting can't be ruled out. I would also check the wires from the crank sensor for continuity, because they feed to the ICM, and if they're going bad or aren't giving consistent voltage readings, it can cause a hard start.

Since you've replaced the crank sensor, it can kind of be ruled out, although there have been known bad ones out of the box. Try and put some dielectric grease in the connectors and see if that helps any.

As far as checking for spark, you can pull and ground a plug and then have someone turn it over and check, but you have to be very careful. The waste spark ignition system is VERY powerful and will shock you pretty badly. Wear some thick rubber gloves when you do this to be safe. Autozone also sells some pretty cheap spark testers, but I've never used one, I just grounded the plugs out on the block.

Also, what's your fuel pressure like? sorry if I missed any test results saying about that, but a failing fuel pump can let the pressure bleed back down after sitting when warm and cause a long/hard start.


edit: just saw that you replaced the "ecm" but the way you described it that was actually the icm. Since you replaced that, I would go ahead and check the continuity on the wiring to see if there are problems there.

Thanks for the additional feedback ... will check.

I have one other theory that I really hope isn't true...that the compression rings are worn, and that when it gets hot, there isn't enough compression to fire....you need three things for an engine to run: spark, gas, and compression. The reason I suspect this:

- low oil pressure based on the gauge. After it is warmed up, I get ~ 30 PSI running and drops to around 15-20 psi at idle. Had to throw some STP oil treatment in it the other day, b/c it was dinging at me b/c of low oil pressure. This cured that problem. currently running 10w30 dino oil in it (plus the stp oil treatment of course).

- engine spins really fast when it is hot (like low compression).
- The PO said he had the intake manifold gasket replaced at one time....if they were running it around with coolant in the oil for a long time this could have done some internal damage.

- It is EXTREMELY consistent about when it does it, how long I have to let it sit, etc before I can restart...like it is following the rules of heat sink and thermal expansion.

The reason I didn't want to believe it, is the miles are fairly low @ 114k, it burns some oil...about 1 qt every 1500-2000 miles...but nothing outrageous. Also, the oil stays relatively clean...so i figure I'm not getting blow by.

Guess a compression check is also on tap.

I would agree - to check out the wire harness between the crank and cam sensor to the ICM. Also make sure the cam sensor interupt is still on the sprocket in the hole.

Not sure if this thread is still active, but if you haven't figured out what is causing the problem I have another suggestion... I never thought of it earlier but I also had a problem like this on my Buick lesabre and that one ended up being a faulty MAF sensor, its something that can be tested with out replacing iirc. Do a search on the forum on how to test the MAF.

The Maf can be tested by unplugging it, then trying to start the car. If it starts and idles better, that could be your problem. Usually though, the MAF doesn't cause a hard start like this, but rather you start the car and it immediately dies, or dies at speed. Not saying it couldn't be the maf, but I doubt it. I think the OP already tried testing/cleaning it though.

The saga continues... but have my fingers crossed for a happy ending.

Two weekends ago I checked the fuel pressure at the rail and it was reading 34 psi...not bad, but below the 40 psi that i've read it should have. Just purchased the car in August, and not knowing when the fuel filter was replaced, decided to do that. Both the fuel line and the brake lines were kinda rusty, and as luck would have it, after replacing the filter I ended up with fuel line leak and a brake line leak. But hey, gained 1 psi on the fuel pressure!

Didn't wan to mess with it, so took it to Midas - they wanted $200 to fix the lines and ANOTHER $250 to replace the wheel cylinders b/c they were weeping. Wasn't feeling it, so brought it home. Spent last weekend splicing in a new metal brake line, and replaced the short section of bad fuel line with high pressure FI rubber line. Replaced the wheel cylinders ... that was a chore - had to cut off the brake bleeder on one side. This was also the first time I wrestled with GM drum brakes with just the one metal wire spring...that was a PITA. Never liked doing drums, but made me long for the old two spring return system.

I also replaced the coolant temp sensor...for the second time (first one I did several mos ago was DOA, put back in the old one). I think this may have fixed it. Gauge is reading a lot warmer than it was...about 220 (may have to replace the radiator, or do a flush). This would explain the killer heat, and possibly the lower than anticipated warm oil pressure experienced since I bought it. So far it has started up fine...time will tell.

Okay - It's better now that the coolant temp sensor has been replaced, it will start, however, it still will idle rough ... it will chug...kind of like a sine wave for about a minute before it clears it throat. It acts like it is rich (although I did replace the FPR) I'm wondering if i have a leaky fuel injector. What would be the best way to test for this?

I haven't seen a post that the TB has been cleaned, only the sensors. If the TB hasn't been cleaned really good, do that. I use super hot water with Dawn dish soap in it, use compressed air to blow it out really good, wipe it down really good, then use TB cleaner if it still looks like there could be any carbon or anything else in the TB. Mine did the same thing yours is for quite a while. Turned out to be a dirty TB, IAC, and TPS. - BC