91 ES rough idle when cold

[4dr92cavi4cyl]

My wife has a 91 Daytona ES 2.5 Auto, no mods other than a new head and $150 fuel pump (ouch!). I bought the car with ~96k on it. The guy I bought the car from teaches/taught a H.S. auto mechanics class locally and he rebuilt the motor at ~80k. When I got the car it seemed fine, but it slowly get worse. When it's started cold it shakes REAL BAD and almost sounds like it runs on three cyl. for a few seconds and idles at about 1500rpm for about 30 seconds then smoothes out. This got worse and worse until the head cracked between the valve seats on #2 & 3. Put a new head on it and it was fine for a week or two. Now it's slowly getting worse again. The guy a bought it from said he put in new rings, pistons, and a crank kit. I think he mentioned the plug wires too but I'm leaning towards the distributor as the culprit.

Suggestions Plz/Thx?

[93_R/T_TT_Stealth]

very possible - check it out - take the distributor off an see if it looks old you can tell by the wear....

[4dr92cavi4cyl]

Well, I'm still stumped. I looked at the distributor and didn't see anything wrong, except for one of the ends (points?) not being pushed through all the way, but I think it was fine because they go in more than enough to make contact. This distributor is weird, I've never seen one where you could pull the points right out of the cap by pulling on the boot, it's like the points ARE on the ends of the plug wires!?

I don't think it was the problem now.

Let me explain what happens when I start it. When I turn the key it turns a few times and fires up then idles around 1500 for a few seconds then the idle drops to around 900 and it gets REAL SHAKY and almost sounds like it runs on three cylinders. After about 10 seconds it smoothes out and runs OK.

It doesn't do this after the first time it's started that day, unless it has sat for hours and hours, WTF?

It has a single injector on the TB, so I know it's not multi-port FI, unlike my Cavy which is MPFI and gets the occasional dirty or leaky injector.

Please give me any ideas you can think of as to why this beast shakes so bad, thanks!

[4dr92cavi4cyl]

28 views, one reply…
No one else has had this problem with 2.5 NA?

[caeanan]

what does it idle at after it smooths out? does it stay at 900 or does it go up or down? do the plugs have any kind of fouling or anything apparent? i dont have any real ideas what it could be but maybe more info would trigger something with someone

[4dr92cavi4cyl]

When everything shakes away it idle's fine at 750, plugs are new!

Actually, when I start it it starts at about 1,500 PRM then as it drops to 900 it's starts to shake and miss. From the time I turn the key till it's smooth and idle's around 750 is about ten seconds, but it's shakes the worst for the first five seconds.

Anyone else had this problem before?

[deranged_one]

When the head was replaced, did you replace the gasket also? My guess is that the head gasket had gone bad, which caused the cracked head. Check the headgasket to see any signs of wear/cracking. When me and my dad shaved the heads on an old 360 we had, the heating of the head caused it to expand and crack the gasket. Maybe you tightened the head a lil too much and it is putting too much pressure on the gasket? This is just a suggestion.. but my spirit with a 2.5 does the same thing, and I'm pretty sure that's a gasket going bad.

[rwood13]

my vote is head gasket, miss would be coming from water in the cylinder, do a compression check and a cooling system pressure check

[4dr92cavi4cyl]

When I had the new head put on we replaced the head gasket, bolts, plugs, oil/filter, coolant, and trans fluid. I had a mechanic do the work so I'm sure he didn't over tighten the bolts. It doesn't blow white smoke or any smoke at all so I don't think that the head gasket is the problem. The exhaust does smell a little rich, maybe it's starting way too rich and it can't fire all four until it leans out. What might cause this?

[4dr92cavi4cyl]

Hmm, IF it HAS been running too rich could that cause excessive heat around the valve seats but NOT cause the motor to overheat due to the fan constantly running?!? When the last head cracked it was a slow process, it took 6 months for it to crack bad enough that it blew the head gasket. My wife was driving when it happened and I was not with her but she said the temp. never went past 3/4. Is the 2.5 crap?

[PWMAN]

Scroll down to the first pic on this page and read-
http://www.thedodgegarage.com/turbo_ignition.html

This sounds very much like the shutter wheel. Also it could be just a bad Hall Effect Pickup.

[4dr92cavi4cyl]

Thanks! Time for a new distributor huh? What is a bad Hall Effect Pickup?

[PWMAN]

Originally Posted by 4dr92cavi4cyl

Thanks! Time for a new distributor huh? What is a bad Hall Effect Pickup?

Eh, if you just super glue the shutter wheel down it should hold for awhile.
The hall effect pickup is the thing right underneath the cap and has two connector's coming out of it and they plug into your wire harness.

[slantsixness]

All jokes aside....

Check the TPS sensor, and the head gasket again.

I can't tell you how many times poor workmanship and lack of education has killed so many 2.2 and 2.5's.

Most "mechanics" and I use that term VERY loosely(and for those of you who might be offended, sorry!) don't know enough to change head gaskets, nothing about re- torquing them, no clue about the machine work that was done, and simply aren't given enough time to do the job, let alone time to learn how to do it right.

In this particular case, the hall effect/shutter wheel or TPS as well as the head gasket can cause this. There are other possibilities too, but these are the most common.

[4dr92cavi4cyl]

I'm NOT a mechanic and I'm not offended, LOL! The guy that rebuilt it before I bought it was an auto tech teacher and I believe he did his part right (should have fixed the dist), I just hope it's a dist prob. As for the TPS I don't think it would be causing the problem because it drives fine, just starts like sh!t. Thanks for the info, I will try these things and get back.