What would cause hesitation when applying gas and rough loping idle when trying to take off and stalling?

BRUCE46

MEMBER
1990 CADILLAC DEVILLE
214,000 MILES

I have a 1990 Deville coupe, 4.5 L engine. The car did run great till about 3 days ago. I noticed some hesitation very slight when taking off.
Now I ve been using Lucas inject cleaner and seafoam regularly and I got about 22 mpg avg. Car was actin kinda lopey on idle so I suspected a bad egr valve as the code e 48 and e 49 came up on my check engine diag.
Took it to a shop and they said it was a cracked diaphram needed a new egr. Ok 258 bucks for it. Wow. Ever since they looked at it it s een getting worse. Now I cant drive it cause it will stall if I try to pick up any speed over 30 mph. Had a new cat convertor installed 3 weeks ago. It has new plugs new alt. New air filter new gas tank new canistor for fumes. Egr is original. Any suggestions? I drive this car everyday and super sweet ride. Hate to have to put her down when I ve got soo much invested

6 Replies

DRCRANKNWRENCH

MECHANIC
3,380 POSTS

There are so many possibilities, I am sending you a diagnostic on hesitation.
It is an excellent sourcebecause it is bery detailed.

Here is the Link, just paste itno Windoes URL bar and hit enter.

https://www.2carpros.com/articles/engine-hesitates

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Saturday, August 27th, 2011 AT 11:15 PM

CADIEMAN

MECHANIC
3,544 POSTS

Test the fuel pressure with a gauge. Then come back.

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Saturday, August 27th, 2011 AT 11:19 PM

BRUCE46

MEMBER
5 POSTS

Ok, so I just went out and took off the air cleaner and started up the car. It ran smooth in idle with that lil lope to it but still was ok. When I put an easy pressure on the throttle, still ok. All the way up to a point was ok but when I tried to give it a quick gun it ran rough and died. Now I sprayed it with some seafoam intake right into the throttle body 3 times and it died. Starts up hard. On 3rd time strat up it fires up and ran great. Took it down the road for 3 miles and it was perfectly fine. No hesitation stalling mnothing. Idle s well still and all. But when I got it shut off I checked the codes again and it threw up code 38 and 41 and 48 49. Any ideas?

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Sunday, August 28th, 2011 AT 5:25 PM

DRCRANKNWRENCH

MECHANIC
3,380 POSTS

KHLow ia a Mater Mechanic, even if the cR RUNA BETTER, YOU SHOULDD STILL TEST THE FUEL PREAAURE. IT CAN CAUSE ALEAN CONDITION AND DAMAGE SENSORS, VALVES, ETC.
AS FAR AS THE sea foam GOES WHEN YOU SPRAY IT IN YOU WILL HAVE TO IDLEIT UP IF YOU CAN WHILE SPRAYING IT IT. IT WILL RUN ROUGH AS THE REMOVED CARBON AND CLEANER DO NOT BURN WELL.
GET SOME sea foam POUR IN THE TANKFUEL SYSTEM CLEANER. IT CLEAN INTERNALS YOU CAN'T GET TOO.

I KNOW Advance Auto Auto and Auto Zone.
You can also borrow specialty tools from there. You put down a deposit and you get it back upon return.

Check the fuel pressure before you do anything becuse there is a reason KHLow said to do it first. Diagnosis is like going through a flow chart. There is an order to testing that makes fining the issue easier and quicker.
Thansk for the help KHLow.

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Sunday, August 28th, 2011 AT 5:47 PM

BRUCE46