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1984 2.5 hard start when cold, poor cold idle by Tony Santucci
Started on: 02-22-2021 06:10 PM
Replies: 10 (79 views)
Last post by: Patrick on 02-25-2021 09:21 PM
Tony Santucci
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Report this Post02-22-2021 06:10 PM Click Here to See the Profile for Tony SantucciClick Here to Email Tony SantucciSend a Private Message to Tony SantucciEdit/Delete MessageReply w/QuoteDirect Link to This Post
Ok. So let's preface this with the fact that I have 25 years of experience as an ASE certified technician and I started at a Pontiac dealer in the '90s!. Obviously, I'm at my wit's end posting to a forum about this.

I picked up an '84 with 89k on the clock. It was all screwed up from the previous hackers over the last forty years. Anyway, I fixed all the blown fusible links and otherwise questionable repairs.

The car runs great when the engine is warm. Cold start is terrible. Either crank no start, or fire and die without some throttle. All the PID data looks good on the scan tool. TPS voltage around .9 volts (a little high for my liking, but it's in spec), MAP appears normal, though it's hard to tell when it's running like crap. IAC counts are around 60 (again, seems a little high to me), ECT appears accurate.

Things I have done so far: Basic tune up (to include setting the base timing properly by putting the ECM in base timing/diagnostic mode BECAUSE SOMEONE WILL SURELY ASK) fuel pump, temp sensor (both, gauge didn't read properly), O2 sensor, pulled the ignition module, cleaned and reinstalled for a no start (grounding issue). The injector is new as well.

It needs to be noted that some potato in the past knocked out the minimum throttle screw. I have adjusted it back to what I think is correct. Hard to say though as there's no real procedure for adjusting a non adjustable thing. I did have one person link me to a procedure for setting minimum idle using a procedure I had never heard of before. I'm going to try that just for kicks.

So that's where i'm at right now. I have a new distributor on the way, because let's face it. The 40 year old one doesn't owe me anything. Also a new IAC is in the near future.

Pretty much everything is going to be new. I'm leaning towards a lazy/non functional IAC.

If anyone has some input, I'm ready to hear it. I'm looking for that silver bullet.
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Tony Santucci
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Report this Post02-22-2021 06:12 PM Click Here to See the Profile for Tony SantucciClick Here to Email Tony SantucciSend a Private Message to Tony SantucciEdit/Delete MessageReply w/QuoteDirect Link to This Post

Tony Santucci

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Patrick
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Report this Post02-22-2021 06:27 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Tony Santucci:

Things I have done so far: Basic tune up (to include setting the base timing properly by putting the ECM in base timing/diagnostic mode BECAUSE SOMEONE WILL SURELY ASK) fuel pump, temp sensor (both, gauge didn't read properly), O2 sensor, pulled the ignition module, cleaned and reinstalled for a no start (grounding issue). The injector is new as well.


I'm aware you replaced(?) the fuel pump, but I'd check the actual fuel pressure being delivered.
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Stingray92
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Report this Post02-22-2021 07:40 PM Click Here to See the Profile for Stingray92Send a Private Message to Stingray92Edit/Delete MessageReply w/QuoteDirect Link to This Post
map sensor was bad on mine, stuck EGR?
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Tony Santucci
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Report this Post02-23-2021 04:46 AM Click Here to See the Profile for Tony SantucciClick Here to Email Tony SantucciSend a Private Message to Tony SantucciEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Patrick:

I'm aware you replaced(?) the fuel pump, but I'd check the actual fuel pressure being delivered.


Yes, the fuel pump is new. I haven't checked the pressure. I was just going on the assumption that it would be OK with a new pump. I'll put the gauge to it though. Only takes a minute.

Thanks!

[This message has been edited by Tony Santucci (edited 02-23-2021).]

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Tony Santucci
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Report this Post02-23-2021 04:58 AM Click Here to See the Profile for Tony SantucciClick Here to Email Tony SantucciSend a Private Message to Tony SantucciEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Stingray92:

map sensor was bad on mine, stuck EGR?


The MAP appears to respond to vacuum as it should. It's kind of hard to tell with the slow data refresh rate. Might replace it anyway, because why not?

I inspected the EGR when I replaced the valve cover gasket. The spring pressure seemed good, and it was not stuck open. I'll make a blockoff plate just for peace of mind though.

It just runs so well warm. If it was low fuel pressure or the EGR was stuck, I'd expect to see that as a lean condition while monitoring the O2.

Thanks!

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Tony Santucci
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Report this Post02-23-2021 07:52 AM Click Here to See the Profile for Tony SantucciClick Here to Email Tony SantucciSend a Private Message to Tony SantucciEdit/Delete MessageReply w/QuoteDirect Link to This Post
It's the IAC.

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theogre
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Report this Post02-23-2021 10:02 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
can still be related to http://www.fiero.nl/forum/F.../HTML/144858.html#p4
ECT w/ "push button" connector often have crap plugs and why no longer made.

FP is 9 to 13 PSI and most gauges won't read this right because made for high pressure systems often max scale = > 70psi

Setting Idle Stop...
See my Cave, Idle Stop
Your 300 TBI need to manually block IAC hole or never get stop adjusted right.

IAC maybe "Bad" but is also trying to "fix" a messed up Idle Stop and can try to open or close "out of rage" to try to adjust.
Often This and others list in this post cause problems Without setting codes.

------------------
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(Jurassic Park)


The Ogre's Fiero Cave

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Tony Santucci
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Report this Post02-23-2021 11:07 AM Click Here to See the Profile for Tony SantucciClick Here to Email Tony SantucciSend a Private Message to Tony SantucciEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by theogre:

can still be related to http://www.fiero.nl/forum/F.../HTML/144858.html#p4
ECT w/ "push button" connector often have crap plugs and why no longer made.

FP is 9 to 13 PSI and most gauges won't read this right because made for high pressure systems often max scale = > 70psi

Setting Idle Stop...
See my Cave, Idle Stop
Your 300 TBI need to manually block IAC hole or never get stop adjusted right.

IAC maybe "Bad" but is also trying to "fix" a messed up Idle Stop and can try to open or close "out of rage" to try to adjust.
Often This and others list in this post cause problems Without setting codes.



ECT is new with the updated weather sealed metripack connector. Fuel pressure was checked with a 100 PSI Snap-On gauge. Reads between 13 and 14
Idle stop is adjusted to 500 RPM with the idle bypass blocked. Should be close enough for the IAC to work with. The IAC doesn't seem to move well near the "closed end" of travel. If I screw the pintle in half way, then start the engine, it starts with a high idle. The ECM drives the pintle towards closed, then seems to lose control of it once it gets the idle around 1000.

IAC is on it's way, and if I'm a betting man that's going to fix it.

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Tony Santucci
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Report this Post02-25-2021 04:52 PM Click Here to See the Profile for Tony SantucciClick Here to Email Tony SantucciSend a Private Message to Tony SantucciEdit/Delete MessageReply w/QuoteDirect Link to This Post
IAC showed up today. That did it.
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Patrick
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Report this Post02-25-2021 09:21 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post

Great, thanks for letting the forum know of the solution. Threads like this can help people down the road with similar symptoms.
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