Like Luca pointed out mic configuration and placement is key. Point around and look for rattles or elements you may want to layer in and use.
It could be great if you can try and find a car that you can abuse a little to produce some sounds.
Maybe loosen a heat shield covering the exhaust under the engine or add a metal plate to induce a rattle.
Pull one of the ignition cables going to one of the spark plugs so that one cylinder does not fire. This will produce a poor idle and engine performance.
Putting holes in the exhaust system and close micing the exhaust can add a layer too
Breaking off pieces of the radiator fan and leaving them hanging will make a horrible sound as well...
Depending on what the image calls for and how far you are able to go with it.
For a comedic engine effect, I often like to use a higher pitched and smaller, struggling engine sound to give off the impression the motor is trying much harder that it should be.
In one film, a character was riding a motor powered bar stool and we wanted to come across this way, so we recorded a small 49cc pocket bike with a heavy driver to give the impression.